It does kind of look like a tan and a little like fert burn. Strange how it's along the veins though. That suggests fert overdose to me. I'm not a fan of the slow release ferts in MG and similar fertilizers. You don't have any control. I would flush it with water and see if it starts to improve. If not then repot but don't go with plain old top soil. That stuff will turn into a brick and choke the plant. Lots of good soilless growing mediums out there that peppers just love.
Good luck.