You may have to play with additive blending since EntityColor is only Subtractive. Working with both may allow to get any color.
At the other hand, to alter the Hue you should convert RGB to HSB in the first place, then you only need to edit the Hue value, or Saturation or Brightness. Tho, convertion is slow:
http://www.blitzbasic.com/codearcs/codearcs.php?code=1380
http://www.blitzbasic.com/codearcs/codearcs.php?code=2072
At the other hand, to alter the Hue you should convert RGB to HSB in the first place, then you only need to edit the Hue value, or Saturation or Brightness. Tho, convertion is slow:
http://www.blitzbasic.com/codearcs/codearcs.php?code=1380
http://www.blitzbasic.com/codearcs/codearcs.php?code=2072