OT: Best anodizing or finish for aluminum heatsinks

[m]

OT as it isn't CFD, but I am sure that folks on this list have
experience with thermal management issues.

I am looking to specify a finish for a forced convection bonded fin
heatsink. All of the CFD work was done on FloWorks with raw aluminum
characteristics.

Now the question is: Which finish degrades performance the least?

Available options are:
Black Anodize
Clear Anodize
Trivalent Chromate

Perhaps there are other options that I should consider, however they
must be RoHS compliant.

Thanks,

-Martin