My understanding is that conventional mica capacitors (not silver-mica) in the "postage-stamp" package were brown or cream colored, but silver-mica capacitors were pink or red. Silver-mica capacitors are more stable and more reliable than regular mica capacitors, but the difference at audio should be negligable. I've found both types sound good in audio applications. The brown epoxy "dipped" mica capacitors are always silver-mica, as far as I know.
- John