Your command will not work as you expected because:
Scoreboard players are shown as UUID if they are not considered player;
Your tag command has an incorrect argument, as @e[type=armor_stand,limit=1,sort=nearest] is not add, list or remove;
The armor stand will not get the tag count if you use the tag command, your tag command tries to give tag to add.
The first reason cannot be fixed, it's how Minecraft's scoreboards work, so your current idea is not possible even if you fixed your tag command. The only way this could be possible is if you used a player - although you will need to change NBT data of the player if you want a space in the name, then you set the player to be in a team and then you could modify the team they are set to, to be a certain color or you could edit the NBT data of the scoreboard, to set the player's name to be a certain color.
Solution
Option #1 (using teams)
team add temporary
team modify temporary color yellow
team join temporary temporary
scoreboard players set temporary <objective> 10
Now close the world and install any NBT editor (if you don't already have one), I recommend NBTExplorer.
Open your NBT editor of choice.
Open up this location in your NBT editor (unless your editor already sets you here): ...\.minecraft\saves.
Go in to your world's folder.
Go in to data folder.
Go in to scoreboard.dat file.
Go in to data.
Go in to PlayerScores.
Here you will see all player scores, you will have to go trough every one of them, until you find your player with the name temporary.
Change the Name tag to: Time Left.
Trace back to data.
Go in to Teams.
Here you will see all teams, you will have to go trough every one of them, until you find your team with the name temporary.
Go in to Players.
Change the only tag to: Time Left.
Save what you've done and exit out of the NBT editor (unless you'll be using it afterwards).
Now, when you open up the world, you'll see you have a scoreboard player Time Left colored in yellow.
Option #2 (using color codes)
scoreboard players set temporary <objective> 10
Now close the world and install any NBT editor (if you don't already have one), I recommend NBTExplorer.
Open your NBT editor of choice.
Open up this location in your NBT editor (unless your editor already sets you here): ...\.minecraft\saves.
Go in to your world's folder (it's a folder with the same name as your world).
Go in to data folder.
Go in to scoreboard.dat file.
Go in to data.
Go in to PlayerScores.
Here you will see all player scores, you will have to go trough every one of them, until you find your player with the name temporary.
Change the Name tag to: §eTime Left.
Save what you've done and exit out of the NBT editor (unless you'll be using it afterwards).
Now, when you open up the world, you'll see you have a scoreboard player Time Left colored in yellow.
Proof
We, firstly, set a random name to have score 10 in the objective, afterwards we set the color to yellow and the name to Time Left.
I am making a map and I was making things about scoreboards.
I made a armorstand first, and I colored the custom name
Command used : /summon armor_stand ~ ~ ~ {CustomName:"{\"text\":\"Time left\",\"color\":\"yellow\"}",Invulnerable:1}
After I made a armorstand, I made a tag
Command used : /tag add @e[type=armor_stand,limit=1,sort=nearest] count
And I used scoreboard and...
this happened :
[ Move faster! ]
a1f83wc-1d96-1ad9-483o-6a54sdf1fe65 10
I still don't get it why does this happen, I can't change armorstand's name and insert it's own name, I can't replace with anything.
Should I remake everything I made and give up about armorstand's color?
What should I do? I think I did everything I can in vanilla minecraft.
Supported for version 1.13.2
Explanation
Your command will not work as you expected because:
The first reason cannot be fixed, it's how Minecraft's scoreboards work, so your current idea is not possible even if you fixed your tag command. The only way this could be possible is if you used a player - although you will need to change NBT data of the player if you want a space in the name, then you set the player to be in a team and then you could modify the team they are set to, to be a certain color or you could edit the NBT data of the scoreboard, to set the player's name to be a certain color.
Solution
Option #1 (using teams)
Now close the world and install any NBT editor (if you don't already have one), I recommend NBTExplorer.
Open your NBT editor of choice.
Open up this location in your NBT editor (unless your editor already sets you here): ...\.minecraft\saves.
Go in to your world's folder.
Go in to data folder.
Go in to scoreboard.dat file.
Go in to data.
Go in to PlayerScores.
Here you will see all player scores, you will have to go trough every one of them, until you find your player with the name temporary.
Change the Name tag to: Time Left.
Trace back to data.
Go in to Teams.
Here you will see all teams, you will have to go trough every one of them, until you find your team with the name temporary.
Go in to Players.
Change the only tag to: Time Left.
Save what you've done and exit out of the NBT editor (unless you'll be using it afterwards).
Now, when you open up the world, you'll see you have a scoreboard player Time Left colored in yellow.
Option #2 (using color codes)
Now close the world and install any NBT editor (if you don't already have one), I recommend NBTExplorer.
Open your NBT editor of choice.
Open up this location in your NBT editor (unless your editor already sets you here): ...\.minecraft\saves.
Go in to your world's folder (it's a folder with the same name as your world).
Go in to data folder.
Go in to scoreboard.dat file.
Go in to data.
Go in to PlayerScores.
Here you will see all player scores, you will have to go trough every one of them, until you find your player with the name temporary.
Change the Name tag to: §eTime Left.
Save what you've done and exit out of the NBT editor (unless you'll be using it afterwards).
Now, when you open up the world, you'll see you have a scoreboard player Time Left colored in yellow.
Proof
We, firstly, set a random name to have score 10 in the objective, afterwards we set the color to yellow and the name to Time Left.