Promotion works with 24bit colour 8 bits per channel and it only has 8 bit colour indexes, meaning 256 possible colours 15 bit is 32000something colours to choose from. and when you work in whatever bitdepth promotion wont let you use colours outside that range.
And why this ¿? i not understand why i can't copy a image with alots of colors(24,32..) and when put in promotion always decrease to 256(workin in 8,8,8)... imagine i would to retouch a photo or anything and when i copy to promotion que quality decrease to much..

In promotion not is possible make gfx with a pallete more than 256 colours?

, well not know for my is very strange, prefer mspaint, i have a image to the clipboard and copy in mspaint with for example 56789 and can working on this.
And i make another proof and copy a image with 63colours with 8,8,8 and promotion change the palette is i mae "use current palette" and if choose "optimizez palette" put dithering in the image (with nearest color actived)
is possible this why i have a evaluation version and this is a restriction ¿?