You can alter it somewhat in the toolset.ini their are color settings for conversation. Not sure if it could be set with enough diffrence. It only does player and NPC colors that I see, but it one of the INI files you can change fonts and scroll speed and that might help as it would scroll thru your chat window slower. Also checking with Bioware the changing color of player or DM names was disabled in 1.65 and not reinstated in 1.66, and serverwide in 1.25 in module builds so the normal answer is now no. This was done because the serverside color change kept crashing the servers. Their are external programs that can do it, but they may cause lag so not really the answer to go with. As I am not 100% sure exactly what your trying to change player or server side I will try to help.
Player side try this I wont promise that it still works after 1.66
You can change the colors used in the converstaion windows (only changes on YOUR system).
Open the NWPLAYER.INI file in a text area and look for the [Chat Colors] section.
Then look for the color section as listed below.
Default Colors:
TalkColor=240,240,240
ShoutColor=255,239,80
WhisperColor=128,128,128
TellColor=32,255,32
ServerColor=176,176,176
PartyColor=240,240,240
DMColor=16,223,255
Color=RedValue,GreenValue,BlueValue - Range of 1 to 255 (You cannot use 0)
Other Colors:
Red=255,1,1
Green=1,255,1
Blue=1,1,255
Cyan=1,255,255
Magenta=255,1,255
Yellow=255,255,1
White=255,255,255
Orange = 255,128,1
Save the NWPLAYER.INI file and your good to go. Just remember other players won't see the colors as this only affects your system. This helps to distinguish between the different things like Shouts, Tells, Whispers, etc.
However this doesn't change anything when the DM is using talk to talk to the group on a quest as the DM char, unless everyone in the party uses party, then party is white, DM as nonparty would be say green. ANd Dm tell's blue. I think DM tell default is green.
Thier might be a scrupting soultion to the server side simular to how you can script the floating text color or damage, system message, etc colors. I'm not sure theirs a seperate setting for DM conversation and would have to look and play around with it, but I don't think so off the top of my head. As I said their are programs that Will allow a player to change the color of their text still but bioware disabled it in the regular game according to biowares site.
Hope the playside fix works for you. If not post again and I will see if their are any other options that I can't think of at 2 AM Hope that this makes sence