Bug report: I just found that when you convert to index it should use the uint8_t type instead of the uint16_t type for the array. This way don't don't have to specify the ColorMode when you declare your Image.
Also, could you update it with the new color palette ? DARKGRAY is now 0x5268 and PURPLE 0x9008
Other nice additions would be that it uses the file name for the variable name, and that it support setting the number of frames for animated Images :)