Both these paint colors were originally formulated for the NSX. Kaiser Silver Metallic was an available exterior paint color for the '97-99 NSX. Solaris Silver was the paint color of the stock wheels on the '94-96 NSX.

These two colors are very similar. However, the texture is slightly different; the metallic aspect of the paint on Kaiser Silver body panels is more prominent (bigger metal particles), although not quite as prominent as the Silverstone Silver Metallic color introduced on the NSX in 2000. The metallic aspect of the paint on Solaris Silver wheels is duller (smaller metal particles), giving them that gunmetal look instead of looking like a metallic body color. I have had '94-96 NSX wheels side by side with '00-01 ITR wheels and they look absolutely identical.

However, both these two paint colors are close enough - and touch up paint on metallic colors is difficult enough to blend - that you won't see much difference in results between either of these two colors when used on ITR wheels. Both are very very close, even though neither is so exactly the same that the touched up portion blends imperceptibly with the original portion. So go ahead and use either one. (I use the Solaris Silver on mine.)

There is no intentional difference in color between '00 ITR wheels and '01 ITR wheels. However, it's possible that the color of wheels changed slightly at some point, which could have occurred even in the middle of the model year and/or when different batches of wheels were produced.