When it comes to celebrities and style, the overriding rule seems to be, “change is good.” This is especially true with celebrity hairstyles; seldom do you see a star’s hair look the same twice at red-carpet and other paparazzi-drawing events. And with a cadre of personal groomers, dressers and stylists on the payroll, it’s not a big challenge for these stars to change up their hair on a regular basis.

While some stars such as Miley Cyrus, Scarlett Johansson and Katy Perry have become known for their mutable hair—going from one extreme cut or shade to another, seemingly overnight—others usually take a more subtle approach, preferring a slight new haircut or variations in styling to achieve a sense of change.

So, when a star makes a significant change in hair color, well, that gets our attention. Here are some of the noteworthy 2015 trends in celebrity hair color that we have detected:

Red hair color

Keratin Complex Amy Poehler red hairPhotos by PR Photos

There’s been a noticeable embrace of the redhead look from formerly-blonde stars such as actresses January Jones and Amy Poehler (above), who has been sporting a very bold red while making the rounds to promote her animated film Inside Out.

Natural brunettes who have recently chosen red hair colors include Rihanna; the aforementioned Scarlett Johansson; and actresses Lena Dunham and Julia Roberts—who have both been spotted in shades of chestnut red hair.

Blonde hair color

Keratin Complex Khloe Kardashian blonde hair

Meanwhile, some women who were noted for a certain color other than blonde have chosen to embrace their inner blonde bombshell. These include actress Christina Hendricks, who dropped her trademark Mad Men red for a becoming shade of strawberry blonde, which is reportedly closer to her natural color anyway; as well as gossip-column staple Khloe Kardashian (above), whose brunette locks underwent a radical change to ultra-light blonde earlier this year, followed by darker, honey blonde.

Not to be outdone, sister Kim Kardashian briefly wore platinum blonde before reverting to darker shades.

Brunette hair color

Cara Delevingne brunette hair

Some celebrities opted to go the opposite way—from natural blonde to a flattering brunette shade. Some of these looks were achieved through a balayage on brown hair for natural-looking highlights. Stars in this category include actresses Blake Lively and Lily James, as well as “It Girl” Cara Delevingne (above).

Unnatural hair colors

We have already reported on the Keratin Complex trend toward bright and bold hair color that celebrities have embraced. Shades of pink have been especially popular, with this look modeled by style icons Madonna and Nicole Richie, actresses Kristen Wiig and Julianne Hough, and TV personality Kelly Ripa, among others.

Kylie Jenner blue hair

But there have also been some very bold color choices among stars, from Empire actress Taraji P. Hensen’s recently Instagrammed purple ombre, to Kylie Jenner’s frosty blue hair (above). For these and other stars, obviously, it’s “go big or go home”!