I tried with 4.3.6.2, 5.3.6.1 and 5.4. I can change text color via Format → Character → Font Effects → Font Color but that’s slow to do.
Writer does have the lower case a with the underscore Font Color icon which leads directly to the Font Color selection. How do I get the Font Color icon to show in impress?
Can’t you (menu) View the Sidebar (Character)? Then it is a one click action to color characters.
Go to View->Toolbars and activate “Text formatting”. That will add text formatting toolbar with all related icons.