This is really basic, but it still needs to be noted. Why? Because red wine and white wines are not the same thing. Once a person understand that difference, then they can start training their palate accordingly.
The difference comes down to the skin. To make a red wine, a vintner will let the juice of the grapes mix with the skins. White wines are made without skins (or seeds). As noted elsewhere… red wine is the outcome of crushed, fermented grapes. White wine is the outcome of fermented grape juice. Why is that a big deal? Easy…grape skins contain tannins that the meat of the grapes do not. It is the skins that give the red wine its color, its bite and its body.
That’s it. That’s the one hard and fast difference. Every other difference between red and white are general rules of thumb rather set in stone dictums.
The “red wine with red meat – white wine with white meat” rule? Eh…more of a guideline. As said before, if you like white wine with beef, by all means drink white wine with beef (and there are some that probably go very well with beef…I’ll discuss that more when I cover food paring).
The “Let red wines age – drink white wines young” rule? Again, more of a guideline. There have been some German whites that have lasted centuries.
The “Red wines complex – white wines sweet” rule? Even less of a guideline than the others. There are sweet and fruity reds and some whites that have had tannins infused from oak fermenting.
My point here is that there are no hard and fast rules when it comes to reds and whites outside of the whole “grape skin” process. The rest depends on the wine varietal, it’s terroir and the process in which the wine is made. But these are 200 level topics to be discussed at a later date.