Both Yellow and Blue Regal tangs need at least 6 feet of swimming space, basically a 125+ gallon tank. Both are equally active. They get stressed and can get growth stunts in smaller tanks.
In a 75 gallon tank, you could have a Kole Tang. I have one in my 90 and it swims around all day looking for algae.
90 Gallon Reef - 3 Blue-Green Chromis, 2 Ocellaris Clowns, 1 Kole Tang, 1 Midas Blenny, 1 Longnose Hawkfish, 1 Zebra Dartfish, 1 Algae Blenny, 1 Six-Line Wrasse
29 Biocube Reef - 1 Chalk Bass, 2 Black and White Clownfish, 1 Yellow Watchman Goby, 1 Fire Goby