Yes, I have never really used these forums, but I am constantly active in working on the pack.
Overall, things are lower contrast and saturation than vanilla. Some things (like redstone for example) are very striking, however. I think it if it something that warrants enough importance, give it that extra visibility.
There are some things I have come to realize over the years, like how the blocks of end stone, netherrack, obsidian, and bedrock were all just stone with the same additional lines drawn over them and then filtered. There is a high level of consistency and repetitiveness in many textures. Thus, I think if you can find a texture to use as a base, you can end up with the same feeling. Bonemouse did release some PSDs of the GUI to work from, but unfortunately no PSDs of the other textures, so figuring out how something had come to be made takes a lot of trial and error and approximation.
You'll also notice that the grass top texture is prevalent in a lot of plant based textures. Vines and reeds (sugar cane, whatever) both come from the same texture. So, once again, reusing textures in new ways is totally Isabella. Sometimes innovation is welcome, but trying to find a way to reuse an existing Isabella texture is not at all an illegal move.
Beveling is a common trait in many Isabella textures. In Photoshop, a soft chisel inner bevel, depth 100%, size 1px, soften 0px, shaded to -45 degrees angle with 30 degrees altitude with global light off, with a 50% overlay white on highlight and 50% overlay black on shadow is a good way to go. Alternatively, using screen and multiply with different values can be used. I think it depends on the texture; Bonemouse probably used both. For ores, using multiply with black pixels on the top and left sides and screen with white pixels on the bottom and right sides, both at 15% opacity, is the way to go.
Just as so, I've discovered some very interesting quarks to textures that hint of just how much of Photoshop was used to create many of these textures. You'll notice a very prominent line in dirt... I believe that may have been the result of using the shear filter over many iterations to "randomize" a base texture to make it look unique yet still give off the same feeling. I might be wrong, but I was trying to randomize some textures with this method for alternate models and I came up with this same line, suggesting that dirt may have been made using the grass top texture (or a texture that they were both made from).
Unlike other packs, there is no predefined palette, but at the same time there are quite a few things that make it distinctive. I am always finding new things that make me go back and revise stuff I've done in the past to put it more in line with the original textures.