I believe I read somewhere there were 72 Black CSL out of the 422 CSL in total for the UK market. U could call BMW Customer Services for the definitive answer

Black is V. COOL colour on the CSL and even though the Silver Grey CSLs are more common, it's my preferred choice as, IMHO it shows off the CSLness (Carbon roof, Duck tail boot, simplified front bumper with the single Air inlet) + the curves of the car, more. It's why they used SG CSL in all the Ad campaign, brochures, Dealer posters, etc..