Open up kotor_tool (or whatever you like to use to explore the bif files, but this works best IMO) and load up the BIFs. When you can, open the tree (click the + by BIFs) and look for "templates.bif" Click that plus, and go way down to find "ptar_sitharmor"
When you get to it, double click to bring up the GFFEditor (you will have needed to DL this seperately and put it in the same folder as kotor_tool is in).
Click the plusses in GFFEditor to open up the trees. Under "PropertiesList", find the "1". Under that, look for "Subtype"
Now.. if your appearance.2da is NOT modified, change the subtype from 28 to 509. If your appearance.2da IS modified (by some other mod), change it to the first number that does not exist in the leftmost colum of the appearance.2da in your override folder. You can check by using kotor_tool and opening the 2da directly from the override folder. If you don't even find one there, it's not modified, and you can just use 509.
Also, at the very bottom of the GFFEditor window, change Tag and TemplateResRef to both read whatever you're going to call this instead of ptar_sitharmor.
Now then.. in GFF Editor, once you've changed this subtype value, click File, Save As. Path your way to the override folder, and give it whatever name you put in Tag and TemplateResRef.
REPEAT all those steps for EACH new color sith armor you want, making the number for the subtype 1 higher each time, and changing the name for the tag etc to make each one unique before saving it to the override folder.
Once you've done that for every color you want to add, you can close the GFF Editor and instead, open your Appearance.2da file (either from the 2da.bif in kotor_tool if it hasn't been modified, or directly from the 2da editor in the override folder if it has.
For every new armor you made, you're going to make a line in appearance.2da. The first colum is just a number, and should be one higher than the last line. It also needs to match whatever you entered for each subtype, so pay attention to which was which or your colors will be mixed up.
Once you have the appearance.2da open, find the line which begins with the number 28. You can highlight this whole line by clicking in the grey box left of the box containing the number 28, and then CTRL-C copys the whole line.
You cannot paste it as a whole line in the editor however, so paste it to notepad as a temporary reference.
Now go to the bottom of the file. In the first empty box on the left colum, enter the number next in sequence (should be 509 unless yours is already modified). In all the boxes across the row, make them look exactly like the line you copied, EXCEPT the following:
Make Label the same as the filename you saved those templates as earlier (one template name per line obviously).
Make the texa field the name of your custom texture file for this color armor. Do NOT include the .tga extention in this field however.
Repeat all that line by line until you've added all the new lines you need (one per new color) and then write the appearance.2da file (save it) to the Override folder.
Whew.. sounds complex, but it's not really so bad. Just follow the steps very carefuly. Sorry for the length and all.. it's a lot harder to explain than to just do it hehe
In game, you'd type "giveitem whatever_you_named_it" with no spaces or extentions. So be sure you named things with underscores if you need spaces in the names (like sith_armor).