Redness in achilles tendons very possible with AS.  Many of us with AS get inflamed achilles tendons, and inflammation is any combination of redness, swelling, heat and/or pain.  I don't think to look at mine until they hurt, and when they hurt, they are also red.  So yes, a person could have the redness even if not in a lot of pain.

About the purple, when I get that in my fingers, it means there is inadequate blood circulating there.  Could be that after your redness/inflammation, your tendons don't get so much blood circulation there for a while.

I have never noticed colour changes, but pain and inflammation in both achillies has been one of the most constant symptoms since this whole thing started over 10 years ago.  I have a physiotherapist give me ultrasound treatment for it and it really helps.  Sadly I suspect the diagnosis period tends to go on for a lot of us.  Good luck.

Hi Maddy,
I have about a one inch diameter lump on my right achilles tendon as well as two small ones starting on my left, with the right side one causing severe difficulting with mobility on many days because of the pain.  I know my rheumatologist said it was all part of the disease process, so I asked whether there was a way to remove them if they get too big and I can't walk anymore.  The answer given after a long pause is that they may be able to surgically remove them in the future if we get to that point???  Do yours have lumps with the coloring and pain??  The pain goes up my leg to the knee and then the back pain shoots from hip to knee....so it pretty much encompass' my entire leg.  How about your pain, does it seem to stretch from foot and hip to knee????  The lumps on my tendons do get red at times but not purple or other colors??
I sure hope you get some relief or atleast find out what is causing the color change.