With the Contax 21mm through 90mm lenses you can also mentally calculate the filter factor and adjust the EI setting. This is offers you slightly more accuracy (or precision?) than half stop adjustments using the EV+/- compensation level which allows only half stops, if this matters to you.
Basically, adjusting the EV+/- will appeal more to perfectionists or the more mathematically inclined (Iam both).
Either system will give about the same results. Playing with the EI suits me best as I limit my filters to UV, yellow, green and orange. Contax G filters came in a limited range (UV, H1, K2, that's about it) and cost a small fortune to buy, I use Nikkor 52mms with a 52 to 46 step down ring. I do not recall ever having used a red filter. I really must try one soon (if only to say I did).