Sadly, there currently is no support for ColorStyles aka named colors in EQ2 script. I've been begging for this from the SOE dev team for over a year now. It remains the one serious hurdle to my "Themes" mechanism and is the primary reason for alternate Motifs like Classic.
As a result, any text color changes need to be made directly to the window xml files. A handful of other elements also use inline color deffinitions that will need tweaking. Most notable are Table objects and graphical item list found in Inventory windows. If you have a batch text processor that won't hose the file encoding, shouldn't be too hard to replace all the color defs. I tried to be consistent
I had hoped to release motifs for several basic font colors but its just too much work to maintain them. I do hope to update Classic by end of year if the gold fonts work with your green theme.
Virtually everything else is defined in _FetishStyles.xml
Photoshop Tips
Layers are your friend. Make a new layer on top. Fill it with the desired color. Then set its blend mode to "Hue" or "Color".
Also try using the Selecttion Menu/Color Range to quickly isolate highlights and shadows. Make a new layer. Fill the selection with a highlight color and set its blend mode.
Save your layered Photoshop file, then flatten it and save to DDS. You usually want DXT3 (Explicit Alpha). 1 bit alpha will save file space if you don't ned semi-transparency.