I'm trying to create a thematic map which can adjust for negative values as well as all positive values. For instance, positive, would be lighter shades of blue to darker shades. For the values that can be negative, such as a change/delta, then I would like to incorporate red shades.
So lets say my darkest shade of blue is RGB(0,0,255) and for each lighter shade I simply up the R and G by a constant. Now what I want to do is invert it so that I can get the same intensity, so to speak, but on the other end of the spectrum. There must be a simple mathematical conversion, but I'm scratching my head with this one. Any help would be much appreciated!