I've noticed that velvet armchairs in purple and royal blue are trendy. I like the look, but are there certain colours and styles that won't look dated in five years?
In the depth of winter, velvet is warm and inviting, but not so tempting in June or July. Over time, it probably won't look dated, but spills will spoil its lustre – velvet requires as much love and maintenance as your hair.
It's interesting that jewel tones such as blue and purple are popular because they perfectly suit the grey that's everywhere. A few years ago, chocolate brown accents partnered well with all that beige. And I once had a professor during the heyday of pink and turquoise who said that brown was a condition, not a colour.
The point: Colours come in and out of fashion, so pick one that pleases your eye and a style of chair that does the same. You'd do well to find an antique armchair that will look good for centuries, with a change of fabric every generation.