The cloth only came in blue or grey and blue corner panel went with blue cloth. The grey cloth models had whiteish anodised aluminium corner panels.
If you have seen red then that will have been a DIY recovering job and not original.
Replacements have not been available even from Lifestyle-AV for a number of years which is why mint examples of these speakers command such high prices.
If like me, you have a mint pair of Lab 5000's, I would recommend that you leave well alone and gaze at the beauty of your appreciating asset.