I find the design of this game very natural and intuitive almost without exception. Both the dice colors and ability iconography work very well. My issue is with the monster colors.
For one thing, we're using colors to represent two different things: dice type and monster level. For another, I don't find anything intuitive about mapping red/black/gold to 1/2/3 experience (XP). The closest I can think of for mapping three colors to the numbers 1/2/3 is bronze/silver/gold and those are terrible simply because bronze and gold are not visually distinct enough.
I think instead we should consider a separate icon on the die to represent XP, maybe 1/2/3 dots (stars?) on the upper left or something similar.
The monster pictures could either be all one color (black?) or perhaps each monster could be a color which reflects it's related power (i.e. fire spell monsters are red) or perhaps their color is simply for flavor (orcs and slimes are green, just because).
If we're really gonna stick with color to represent XP, maybe we can find a better color scheme, something more intuitive. Green and blue are frequently used for safe while orange and red for danger so maybe something like green/blue/yellow/orange/red for easiest to hardest, with yellow/orange/red corresponding to 1/2/3 XP?