That redness is from increased hormone levels, somewhere around 14 to 18 weeks -- along with crowing, maybe aggressiveness, etc. At least that's about the age for regular old large fowl such as Barred Rock, etc. I don't know anything about Seramas, sorry. You will find threads about Seramas in our Breeds forum, though.
My Serama roo's comb and wattles started turning red at about 4 weeks old. He started crowing at about 5 weeks. I don't know if this is normal or not for them. I do have other roo's in the vicinity that crow all the time so maybe that's why he started.