Based on the image filenames (IMG_1234) it appears you are shooting in JPEG mode. When you blow out hightlights AND you shoot in JPEG, your image is toast - you will never recover the lost info. If you had shot in RAW then you could recover your blue sky in the raw conversion software (e.g. Lightroom). Also note that when you shoot in RAW the white balance setting is mostly irrelevant, because you can change the white balance in the raw converter.
It also appears that your camera’s light meter is off - all your photos (even the one without people, with the nice blue sky) see a bit over-exposed (to me). I have 2 cameras that are a bit off - one I regularly shoot with EV +1/3 stop, the other with EV -1/3. Your photos will have more color, punch, depth if you set your EV to -1/3 or even -2/3 (try both, see which produces photos YOU like more) all the time, even when you are not using flash.
To precisely control the flash for flash fill, I suggest you take a non-flash photo first using TV mode (so you can control the shutter speed, keeping it at 1/250 or lower where it will sync with your flash) and make sure you like the exposure settings for the background. Then set those settings in MANUAL exposure mode, and let the flash do the flash fill automatically while you precisely control the exposure of the background. When you let the camera adjust both the exposure (using any exposure mode *other* than Manual) and the flash it will always give preference to the objects which are receiving the flash’s light and the exposure chosen for the background may be incorrect (in either direction).
Finally, as someone else noted upthread, your white sky photos are shot more directly towards the sun, and the blue sky photo was shot 90 degrees from the sun. If you set your camera to manual exposure and take a series of photos to make a 360 degree panorama, you will illustrate to yourself how much the light value of the sky changes as you change the orientation of the camera to the sun. I suggest you do this as a practice exercise to help you "see" how much the sky gets lighter and darker as you change your angle. Once you see it in the photos you will learn to see it with your naked eye and make better photos.