There are a few reasons for this.
In my older photos, before I got a flash, I relied on available light. This usually meant very warm tungsten bulbs, which cast an orange hue across everything. I usually adjusted for this either via my camera's white balance or in post production. During that period, I actually preferred cooler tones and often over-compensated for the white balance.
Now that I have a flash this isn't usually an issue. Flash bulbs are fairly well color balanced (they're actually a tad cool, but usually the camera compensates for that). However, the flash isn't the only light source - and so depending on the camera settings, the flash may be competing with other warmer light. In addition, in this particular set, the ceilings were painted warm colors and thus the flash inherits those hues when bouncing (typically you bounce flash off a ceiling or wall).
I universally cooled down the colors on this set, but not so much to lose the natural feel of the environment (which was very warm). Warm colors also tend to be more flattering for portraits, although they can also wash out the colors and so I try to find a balance. In this set, I think the photo of Katie is a tad cool and the photo of cat women is a tad warm.
Last, you'll often notice that the backgrounds are very different in color than the foreground. Sometimes this is because of painted walls. In addition, though, this is because the backgrounds are lit by different sources which usually are warmer than the flash. Professional photographers will often light the back ground independently of the subject, which has a number of benefits one of which is to ensure that both are being lit with comparable color temperatures.
Last, if you're shooting in film, you can adjust for these items using filters or film. When I shoot with my medium format camera, for instance, I use a film that is color balanced for portraitures - which means it's a bit warmer. Indoor vs. outdoor film is similar (indoor film tends to be cooler, to compensate for the tungsten bulbs). Likewise, there are filters that will compensate for available lighting or, provided balanced lighting, warm up the subject.