In the Scott Specialized Classic Cat.:
#135 for Two Pence Violet - $0.70
#136 for Two Pence Violet-greenish - $17.00
#137 for Two Pence Violet-buff - $17.00
#137A for Two Pence - Violet-Lilac $ 475.00 (very rare!).
Here the big problem is to identify the colors, sometimes the color through the scanner is a bit altered, you need to check and compare the color with another stamps of the same Country.
I hope this helps!