Short answer
Start with navy (works for everything), then charcoal (more formal), then expand into mid-grey, tan and beyond. The first two colours cover 90% of occasions.
Navy — your first suit
Works for business, weddings, dinners, interviews and funerals. Pairs with every shirt and shoe.
Charcoal — your formal anchor
Darker and more formal than navy. The colour for board meetings and winter.
Mid-grey — the versatile third
Lighter, works day and night. The best colour for showing texture.
Beyond the basics
Tan for summer, midnight for evening, brown for country. Each adds range but reduces versatility.
Questions people actually ask
What colour suit is most versatile?+
Navy. It works for every occasion, pairs with every shirt and shoe, and photographs well.
Is black a good suit colour?+
Black reads formal and can look severe in daylight. Navy and charcoal are more versatile.
How many suit colours should I own?+
Two covers 90% of occasions (navy + charcoal). Three adds range.