What is the geographical location?

Southeast Virginia

Since it's a yellow form perhaps it is sun burn, if you have had any markedly hot weather. Because other yellow foliage variants of other kinds of plants can be prone to it, and not because I know anything about yellow sweet potato plants having a problem.

Also that dark mulch might be radiating heat around the plant, causing damage that would not be seen in another situation.

As for bugs such as mites being possible check by getting a magnifier and looking at the undersides of affected leaves. And doing a web search trying "yellow sweet potato pests and diseases" or "problems" - with so much content on the web these days something specifically relevant might actually come up.

Thanks for your insight! I do have the sweet potato vines in planters as well, and they look the same way. So I'm thinking it's not due to the mulch. It hasn't been super hot here, and I haven't been able to appreciate any pests. Do you know if watering the plant during afternoon sunlight would cause sunburn?

Watering does not cause sunburn or scorch......too much sun does :-)

when were they planted ... perhaps they are perennial for you.. but for me.. they are warm annuals ....

if you just bought them .... did you harden them off to sun before slamming them into the sun???

often.. we dont know where the plants came from ... perhaps a greenhouse.. so when you get them home.. you need to harden them off to full sun.. just to be careful ...

did you apply any water sol fert after planting.. that can also burn tender young foliage ...

i would probably just watch them for a few weeks ... and then look close.. and see if new growth is unaffected .. and if so ... then the problem may have just been transplant stresses ... plus that above ...

ken

ps: i had trouble with black or dark mulch.. but that was more of a high heat of summer problem... when it accumulated and retained heat .. late into the night.. basically causing a watering problem during the day ... and the slow night time recovery period ... i wouldnt expect it to be a spring problem ...

I purchased and planted them about 1.5 weeks ago. They were located in a greenhouse when I bought them. I think you're exactly right....I never transitioned them to full sun! Thanks for your help!