I am very partial to the yellow legs. It's such a vibrant color to match the vibrant colors that Serama's can come in. If you show at the Cajun Classic, the leg color isn't as likely to be an issue as with APA or ABA. Type over leg color at Jerry's. I have some of both but the deeper the yellow on the legs, the better I like them.
I like both the dark yellow and the swarthy legs. I think there might be a time when I would prefer the lighter legs, depending on the Serama's feather colors. If you had a washed out diluted leg on a colorfully feathered bird, I don't see a lot of people thinking that was attractive and when you show, it's about being correct but also about being attractive, eye popping and a washed out color isn't as likely to attract attention. Green is kind of cool with the right feather colors but not correct either so I sold my 2 little green legged pullets. It was actually kind of a weird look with their plain brown feathers anyway but I've got Araucana's too and willow/green legs are correct with certain varieties.
I wasn't sure I thought pale legs were so bad but when I started hatching out better leg color, wow, I think it's very eye catching
I think paler or at least slate legs look okay on blue but even they have more wow if the legs are darker. I have some black chicks with very black legs and some with swarthy legs. I'm sort of torn. The black legs are kind of cool looking but then when I see other breeders black Serama's with dark yellow legs, again, wow....very appealing to me. I will be breeding my chocolates towards dark yellow with minimal swarthy-ness but deep yellow legs on a solid chocolate is really, really nice.
Even in the wild bird world, the more vibrant is generally the choice when choosing a mate
Cathy