(2^25) * 3 = 100,663,296

This is mine

Actually in 1 pixel there can be 4 colors as empty is one too and there are 3 others so 2^25*4=134,217,728 different combinations
And yes I just changed my icon to all empty colour just to test it

No, the pixels can either be a color of your choice or blank

Yes, my wording was poor, but that is what I meant and with a secont thought I would correct myself, cause you can chose only 1 color and leave blank pixels that way, so this is more interesting now...
- totally blank: 1 possibility
- with 1 of 3 colors, at least 1 pixel colored: 2^25-1=33,554,431 possibilities (-1 is the completely blank one)
- all colors: 3*(2^25-1)=100,663,293; +1 (the completely blank)=100,663,294 total possible custom icons. (You counted the blank one 3 times with each possible colors.)

k