You're able to change label,dice, outline, and edge. colors when you arent using a theme. Themes are premade. Not using a theme will allow you to to customize the set as stated under theme "if you prefer a custom color selet "custom" in this list. This lets you change the colors at the bottom.
Perhaps a silly question, but can you set specific dice to specific rolls? For example, you're casting a fireball, you click the fireball button and it rolls a fire-themed die for hit/damage, and you keep whatever settings you have for your "normal" rolls?
Not a silly question at all! The answer is a bit of yes and a bit of no. So you can roll different looking dice based off damage types! If you type [DAMAGE TYPE] (for example [fire]) at the end of your roll, the dice rolled will have a fire themed texture! You can also input this same damage type tag into any of your spell and item damage formulas so you don't have to manually input it every time! On the downside, you can't customize which texture is used when using the damage type tag. That is defined under the hood and we as users don't have access to it.
There’s a module called Dice Tray which adds buttons for all the different dice under your chat box so you can just click them instead of writing in the chat box.