Hey does anyone know why some titles are blue and some are yellow under the popular manga ...

I'm curious too cuz it doesn't match my read/tbr list

Yellow means recently updated.
Blue I'm not sure, i think it means that the work is completed

for completed ongoing there's a little emoji next to the name too

Yellow meaning it was recently updated makes a lot of sense actually

Yep for the yellow I'm a 100% sure lol