Need to figure out what this rust coloring on my l...

It probably was over watering. let the soil really get dry before the next watering, that will promote a healthy root system.

Nutrient lockout from excessive watering. Don’t feed anything to a seedling in soil till at least 2 weeks old of healthy growth. Unfortunately if she’s older than 14 days in my experience she is not growing at the moment. Just looking at your soil confirms she’s drowning in her pot. Put her somewhere she can dry. If you add another layer of dry soil on top it could wick some of the moisture out of the overly wet soil below. Your not going to have to water that for at least 5 days maybe more. It’s easier to kill your plant by overwater than under. Let her dry out ASAP! Good luck

Allright mixing your own soil is a good idea. BUUUUT...... taking the right ingredients is better. My advice for you make a new mix and avoid the blood meal.. that is to much nitrogen for such a little beauty. my soilmix is... 2 parts humussoil, 3 parts moss peat. 1 part perlite 1 part vermiculite. you get an ph of about 6to 6.2..... humus gives microbes and food, peatmoss gives you watersaving and loosens the soil. perlite makes it fluffy and vermiculitestables the ph......pic out that unhappy girl give her new soil (ready prexixed) or an own mix. i hope she recovers because the causing of nitrogen you see days later,, happy growing

Looks like your nutrients don't come to your plant... Nitrogen is blocked so my advice is to change thz container and give it a bigger pot with fresh new soil.. Keep your PH range at 6/6,5, and in one week she will have recover !

Hey bud this looks like pretty textbook cal/mag deficiency possibly caused by potassium burn. Do you have a micronutrients solution or cal/mag+ solution you can add? Go real easy on the nutes at this stage, although I do not think you have any nitrogen problems yet. Good luck!