In 2001, when Jim Markham started Pureology in Irvine, California, most shampoo was built on sulfates, the strong detergents that make a big lather and also pull color out of dyed hair. His idea was simple and a little radical for the time: a professional line made specifically for color-treated hair, with no sulfates at all and entirely vegan formulas. L'Oréal bought the company in 2007, and sulfate-free shampoo, once a niche idea, is now everywhere.

Pureology Hydrate Shampoo is the one most people start with, and it is still the clearest expression of that idea. It is a moisturizing, color-protecting shampoo with jojoba, green tea and sage for medium to thick, dry hair. It is also very concentrated. The brand says one bottle gives more than 75 washes, so a small amount goes a long way.

Here is a test I like with any color-safe shampoo. Wash with it for two weeks, then look at your towel after drying your hair. If you used to see a faint tint of your color on it and now you do not, the shampoo is doing its job.

The first grid is the Hydrate line, including the lighter Hydrate Sheer for fine hair, plus the mask, oil and leave-in that go with it. The second grid is the rest of Pureology, for hair that is damaged, frizzy, flat or blonde rather than simply dry. Between the two, almost every kind of colored hair is covered.

The first decision is simple, and it comes down to thickness. If a ponytail feels substantial in your hand, you want Hydrate. If it feels thin, or your hair goes flat by the afternoon, you want Hydrate Sheer.

The original Hydrate Shampoo and Conditioner are the richer pair, made for dry, color-treated hair of medium to thick texture, and the conditioner also softens frizz and protects against UV. Hydrate Sheer is the same idea made lighter, a silicone-free shampoo and conditioner that give fine hair moisture without weight. Like every Pureology shampoo, both are sulfate-free, and both use the same trio of jojoba, green tea and sage.

Then the extras, which are where Pureology quietly shines. The Hydrate Hair Mask uses camellia seed oil and vitamin B5, detangles instantly and gives up to 72 hours of hydration. Once a week is plenty. Glow Catcher is a lightweight oil for dry, frizzy lengths, and the brand says it adds 158 percent more shine. Use a drop or two on dry hair, never at the roots.

Color Fanatic is the one I would not skip. It is a leave-in conditioner and detangler that primes hair before styling and protects against heat up to 450°F, with camelina, coconut and olive oils. If you blow-dry or use an iron, it earns its place. The gift set is the easiest start of all, full-size Hydrate Shampoo and Conditioner with a travel-size Color Fanatic.

What I would skip: the regular Hydrate Conditioner on fine hair. It is made for thicker hair, so go Sheer.

If your hair is not simply dry, one of these lines probably suits it better.

Strength Cure is for damage, the hair that snaps when you brush it or feels rough after bleaching. The shampoo is vegan and sulfate-free, with plant-based proteins and astaxanthin, and it is built to strengthen as it cleans. Strength Cure Blonde is its purple sibling, which tones brassiness and fortifies lightened hair at the same time. The Dream Healer Serum finishes the job, a weightless serum that seals split ends and protects against heat up to 450°F.

Smooth Gloss is for frizz. The shampoo is made with amino acids and, the brand says, boosts shine by 50 percent while it smooths. Pure Volume is for fine, flat hair, a lightweight shampoo with wheat protein that clears away buildup so roots can lift. Nanoworks Gold is the most indulgent of the lot, a rich shampoo with golden marula oil for very dry, dull, brittle hair.

Two finishing touches. The Color Fanatic Top Coat is a clear gloss with oat milk and camellia oil that brings back shine when color starts to look flat between appointments. Love Luster is a hair perfume, vanilla and peony with bergamot, made to be safe on color-treated and dry hair.

Here is a pairing I like: Strength Cure Shampoo with the Hydrate Conditioner, if your hair is both damaged and dry. Mixing lines is fine.

What I would skip: hair perfume sprayed close to the roots. Mist it on the lengths from arm's length.

I think Pureology Hydrate Shampoo has lasted for the same reason the brand started: it takes color seriously without being fussy about it. Dry, thick hair gets Hydrate. Fine hair gets Hydrate Sheer. Add Color Fanatic if you use heat, and that is honestly a complete routine.

Everything else here is for specific problems. Give the basics a month before adding anything, and let the color on your towel, and in the mirror, tell you whether you need more.