Mary's vs. Laura's physical appearance question....

Same actress obviously, but she looked really difference as Laura vs. Mary Richards even though the shows were only a few years apart. For instance:


Mary Richards looked much darker in complexion than Laura Petrie. Would this have to do with the fact that MTM was in color and DVD was in B&W? Was MR's darker complexion due to Mary's getting a lot of sun tans or did they just use dark makeup?

MR also looked skinnier than LP also and much older than just the 4 years between shows.