Now im no sensitivity expert. but why is it that when i make my dpi Really high the sensitivity goes from green to a lighter green. when going from 1200 DPI, 6 sense in BF2042 (Ingame sense) then convert it to 3200DPI . 

The color will change from green (perfect match) through orange (about 2% off) to red (about 4% off) depending on the discrepancy.
The discrepancy is the difference between a perfect match and what you actually get due to limitations in rounding.

The only way to fix this is to either use config file sensitivity with more decimals supported, or to fine-tune your DPI if your driver supports it (or through a 3rd party program).

You can see the required DPI for a perfect match if you set the calculator mode to "Advanced".