If your goal is to warm up the space, there are an unlimited amount of rich colors that would enhance white cabinets and appliances. Depending upon whether you want the space to remain in the "neutral" family of colors, terracotta would be a lovely choice that would contrast with the whites, as well as highlight the taupe that exists in some of your floor tiles. You may consider painting only an accent wall to begin with. Then, if you are satisfied with the resulting color, you can always paint the remaining walls.

Another option is to go outside of the neutral family and select a different shade of warmth for the kitchen space. You would probably be most satisfied selecting a hue that you already like, and can live with viewing on an everyday basis. Some examples of up to date warm colors would be mustardy golds, rich cranberry, spicy cinnamon or the chocolate brown family (such as toffee, mocha, etc...). You may even decide to use one of these hues as an accent color, to highlight the terracotta that you are already considering. Terracotta can be the primary color (used for the walls) and another shade (such as mocha) can be a highlight color (used for decorative accents, such as window and door trim or a painted border). Consider consulting with a paint expert at your local home improvement store for assistance with selecting hues that represent the same intensity of color, so all colors in the kitchen space will blend graciously.

Regarding your second question, whites are becoming particularly popular again. Many paint manufacturers have recently introduced paint lines that are only whites- but may be highlighted with a specific hue. A good idea is to explore the various paint chip samples of white, then narrow down your search to 3 or 4 hues that you like best. Consider purchasing a small container of each paint, then bringing them home and actually applying them to the walls in various rooms. This way you can view what they look like in natural sunlight, artificial light and with the other colors that exist in the space.