in the cover of volume 7 seras is depicted with yellow uniform, though it only showed the upper, the ova included in brown gloves, white stockingm brown boots and red armband, the uniform still stayed yellow, i think it would be better to follow the ova for reference for most fans agrees to it rather than the anime version which is blue uniform....

(though her eyes in this outfit varies with her emotion, she almost always sports a set of blue eyes, but when she is full of rage/excitement like when she bombarded the zeppelin her eyes turns to red like the image above)
the red one (red uniform, darkred/black stocking, white gloves,white hair, and left arm being wing shadow like, red eyes) is her uhmm i would say true vampire form which was unleashed when she fed upon pip
RED... both the yellow and red schemed uniforms can be seen in the ultimate ova... :3 hope i helped you :3