Drawing specific RGB on touch screen
As noted in the second paragraph on Adafruit's Graphics Library webpage, 


  First thing to note is that color is 16-bit, and that includes Red, Green and Blue in a 16-bit variable. The way the color is packed in is the top 5 bits are red, the middle 6 bits are green and the bottom 5 bits are blue.


If you want to specify 8-bit color components, you could write an intermediary routine to translate from that form to the 565 form.  For example:

#define rgbDrawPixel(x,y,r,g,b) drawPixel(x,y,(((r)&amp;0b11111000)&lt;&lt;8)|(((g)&amp;0b11111100)&lt;&lt;3)|(((b)&amp;0b11111000)&gt;&gt;3))


Note, this assumes the TFT library you're using has the same specs as Adafruit's.  That might or might not be; I don't know how to account for a 255 color number showing up as blue rather than white.