To change the Barbs to white, go to ...\Assets\XML\ and you'll find a file called CIV4CivilizationInfos.xml. You can open it with any text editor (e.g., NotePad). Scroll down well towards the bottom and you'll see:
Code:
<CivilizationInfo>
<Type>CIVILIZATION_BARBARIAN</Type>
<Description>TXT_KEY_CIV_BARBARIAN_DESC</Description>
<ShortDescription>TXT_KEY_CIV_BARBARIAN_SHORT_DESC</ShortDescription>
<Adjective>TXT_KEY_CIV_BARBARIAN_ADJECTIVE</Adjective>
<Civilopedia>TXT_KEY_CIV_BARBARIAN_PEDIA</Civilopedia>
<DefaultPlayerColor>PLAYERCOLOR_BLACK</DefaultPlayerColor>
Change "PLAYERCOLOR_BLACK" to "PLAYERCOLOR_WHITE".
Similarly, you can change the English from white to some other colour.
Not everything is that easy.