During high traffic chatter, if there are different conversations it is very hard to follow and differentiate. Would be nice to have the option to change the color of text of greenwall generated guild messages

I see. In that case i suppose this suggestion is moot. Thanks anyways.

Greenwall doesn't perform any chat formatting, it sends the messages to the system to display. Conditional formatting of the chat messages displayed would have to be added in a addon like Prat or ElvUI.