Red and black work because black makes red look even more vivid. It is a powerful pair, linked to passion and elegance. It works especially well in fashion and for brands that want to grab attention.
Use black as the base and red as the accent, for example 70-30 or 80-20. In fashion, a black dress with red lips or red shoes is a classic. At home, use it carefully: a red armchair against white with black details beats dark walls. Add white or gray to let it breathe.
Contrast between them: 3.2:1. If you put text in one color on the other, use large sizes only.
Yes, if there is plenty of white or light gray to balance it. Use red on one piece of furniture or pillows and black for details.
A bold true red or a wine red. Wine is more elegant; pure red is more eye-catching.