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Oxide colors get a bit weird on stainless steel, since, you know, they aren't supposed to oxidize. I really only use the oxide colors as a backup method to make sure I had the right tempering temperature, a well calibrated method of heat control is really all you need.
Back to the hardness files, jimm does bring up the very solid fact that they do jump in increments of 5, so the results won't be quite as accurate. As I already said thoughts, my personal opinion is that knowing the exact rhc is unnecessary, and ballpark (within a few points) is good enough. I also believe that files are a perfectly serviceable way of getting inside the ballpark, when combines with the data sheet for whatever steel I'm working with.
In my case, I work primarily with 1095. I know that 1095, properly heated and quenched in appropriate quenchant, will reach a Max hardness of about 65rhc, which is about as hard as steel gets. I also know thats more than hard enough to prevent your average metal file (typically 61-63rhc if memory serves) from biting in. According to the data sheets, tempering full-hard 1095 at 450 should bring the hardness down to about 60-61rhc, and at that point a file should just barely bite into the steel. Bring the tempering temperature up and the hardness down to the 57-58 range, and you can feel the change in how the file bites into the steel. Its subtle, but there enough to notice.
Is it perfect and accurate to withing a point? No, not at all, if you need within a point of accuracy you should probably invest in one of those $1000 hardness testers. It is, however, accurate enough for my needs
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