Single-Process Colour (aka Base Colour)

Single-process hair colour is what you want to ask for at the salon if you want an all-over hue update. The hair is just one tone from scalp to ends. It's also referred to as a base colour. For covering grey hair, a single-process is all you need.

Double-Process Colour

A double process is a base colour plus highlights. Make sure to book additional time at the salon if you want a two-step hair change, which looks more natural in the end. Double-process has gotten a bad reputation over the years, but it doesn't have to be unhealthy for the hair when done by a professional.

Highlights

"[Highlighting] is the act of lightening pieces [6] of the hair with the use of colour or bleach and folding them into a foil to let the colour process," celebrity hairstylist Clariss Rubenstein [7] previously told POPSUGAR. "Typically, there is a structured pattern the colourist follows when applying highlights."

Maria Elizabeth [8], hairstylist and owner of Salon deZEN, added: "Foil highlights start directly at the roots of the hair to create anywhere from lower contrasting highlights called babylights to highly dimensional hair colour. The amount of the contrast is visually created by taking larger or smaller sections and not just by making the hair itself lighter."

Lowlights

Lowlights are the opposite of highlights. They are darker pieces of hair usually reserved for the layers underneath and around the neck. "If kids are out in the sun, the top of their heads get really light and the middle, back, and under are always darker because that part doesn't see the sun," said Hill. Lowlights can also be used if highlights have morphed into one solid colour over time. "I call it the buildup of highlights," she said. "If you go every six to ten weeks, and get highlights over and over, eventually you will probably need some lowlights to break it up because things just get solid."

Babylights

"[Babylights] are placed around your hairline and on your part," Hill told POPSUGAR. It doesn't go too deep within your hair. "Just think subtle, delicate — and it's good for fine hair." Think of it as taking small pieces of hair and only highlighting the top half of it.

Ponytail Highlights

If you like to wear a lot of updos, Hill recommended adding a few ponytail highlights near the nape of the neck and over the ears. "I think it's good to keep some highlights around the whole perimeter of your head because it seems lighter without doing full, internal highlights," she said. "When you lift [the hair] you have just the few highlights over the darkness, and it looks natural."

Bronde

"Bronde" is what you call the hair colour in between brunette and blond. Hill described it as taking someone with dark blond or light brown hair and adding a layer of highlights to lighten the overall colour.

Balayage

When you see the colourist at the chair next to you meticulously painting every strand of hair with bleach, that is balayage. In French, the word means sweeping or scanning. It's just a myth that balayage always looks more natural than a foil highlight. "If [the colourist] is being heavy-handed, someone can end up with these chunks right on their hairline," Hill said. "You shouldn't be able to tell the difference between a good balayage and a good foil, in my opinion."

Rooting

If your schedule won't allow hair colour appointments every six weeks, ask your stylist to root your hair. "We do all the highlights, and then we put a gloss, or a toner, or a colour on the roots to tone it down," Hill said. "It's just something that takes away the contrast so it doesn't look so bold or blatant in the regrowth. I like to compare it to smudging your eyeliner."

Ombré

Ombré trends every summer when people want sun-kissed hair that is dark at the roots and lighter on the tips. The real beauty of it is how low maintenance the style is. "When it first came out the idea was to lighten up just the ends, and it looked natural because on a child hair goes from dark to light on a strand," Hill said. "It's like a beachy brunette, pretty and subtle."

Dip Dye

Dip dye is the most extreme form of ombré hair colour. There is a clear demarcation where one colour ends and the other begins. This high-contrast technique is definitely for the bold, and it looks fabulous with bright shades [9] especially.

Sombré

Hill described sombré (subtle + ombré) [10] as the marriage of typical ombré hair colour with babylights. There are some highlights near the roots, but the majority of the colour is still at the ends.

Tortoiseshell

"[Tortoiseshell] is more highlighted than sombré, and it's less ombré than ombré," Hill said. "It basically adds more highlights to the top portion of the hair and it makes the ombré even more subtle." The key to getting the tortoiseshell look on brunette hair is to ask for golden tones. Key words to use with your colourist are honey, caramel, and copper.

Spongelights

"Spongelights" are highlights with a sponge. It's a new emerging trend that's just barely started in salons, but pretty soon it will be the talked-about technique. "It's a form of hair painting," Hill said. "You apply colour with a sponge and it just touches the surface of that hair, so you're not penetrating it." The effect is sun-kissed, barely-there colour.

Oxidation

When your colour just doesn't look as vibrant and it's time for a touch-up, it's probably the fault of oxidation. And blondes aren't the only ones who get brassy. Oxidation can happen to brunettes and redheads, too. "People think it's the sun that oxidises, but it's just the elements: hard water in your tap, shampoo, conditioner," Hill said. "Permanent colour, in general, has an expiration date."

At around four weeks when your hair colour starts to turn, book a toner, gloss, or buildup remover with your salon (and a conditioning treatment, too). At home, make sure to use a colour-correcting shampoo and conditioner — it's not just for blondes. According to Hill, brunettes with ombré hair colour and highlights can go brassy, too. The goal is to stay nice and cool, like Margot Robbie pictured here.