Hi, I'm writing a mapbasic program that gets a "start colour" and and "end colour" from the user, then works out gradational colours between those two  - exactly the same as the range tool in thematic mapping utility.  (No I can't use that, so yes, I'm re-inventing the wheel).  So far I've got the code to work out the number of colour variations required, and has worked out the numeric increment that is added to the "start colour" RGB value to create a succession of new colours.  It works - i.e. I'm sort of seeing a colour variation, except that I'm getting a variety of tones (i.e the brightness of the colours isn't gradational), which doesn't look quite right.  Anybody gone through this process before?  Or know of a decent resource that will explain the use of RGB values?   (I've read the MapBasic manual - Red x X, Green x Y etc), but I haven't found that helpful.
 
TIA
 

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