First, they weren't all beige - there were plenty of shades of pale grey, pale brown (beyond beige), and white in use. Three colours in particular were very common:

1. IBM's "putty", which IBM used on a wide range of products.

2. Apple's "Apple beige", introduced on the Apple II.

3. Apple's Pantone 453 beige, introduced on the Macintosh.

Pale neutral colours like this were standard at the for office equipment such as typewriters, word processors, photocopiers, etc. These colours didn't clash with other office equipment or office furniture (which was also usually in similar colours). Beige and other browns, and greys, were preferred over whites because dirt and fingerprints didn't show as much, and age-yellowing of plastics wasn't as visible. When personal computers became common office equipment, they came in typical office equipment colours. Apart from matching the rest of the office, having computer equipment in the same colours as other office equipment made it seem less special and scary - important when people new to computers had to switch from, e.g., typewriters and word processors to personal computers.

Early home game consoles (video game systems) came in a wider variety of colours. Some were beige or other pale colours, many were in browns and blacks to match TV colours, some were black-and-silver, and a few were bright orange or red. Game consoles form part of the ancestry of home computers, and their colours resulted in some early non-beige/pale computers, such as the TRS-80, VideoBrain, and the Sinclair ZX Spectrum:

• https://commons.wikimedia.org/wiki/File:Radio_Shack_Tandy_TRS-80_Model_I_System.JPG

• https://commons.wikimedia.org/wiki/File:VideoBrain_Family_Computer_-_Front_View.jpg

• https://commons.wikimedia.org/wiki/File:ZXSpectrum48k.jpg

Thus, home computers in various colours were already appearing in the late '70s and early '80s.

The IBM ThinkPad of the early '90s:

• https://en.wikipedia.org/wiki/File:IBM_ThinkPad_701C_keyboard.jpg

is often described at the first foray by the big brands into the broader universe of colours, but it was not the first black laptop, preceded by the GRiD Compass 1101 and the Dulmont Magnum (the first true battery-powered laptop, and the first-and-only Australian laptop):

• https://history-computer.com/ModernComputer/Personal/Grid.html

• https://collection.maas.museum/object/365015

Finally, Apple brought freedom of colour for computers into the workplace with their iMac in 1998, originally bright blue, and later joined by more colours:

• https://commons.wikimedia.org/wiki/File:IMac_G3_Bondi_Blue,_three-quarters_view.png

References:

A graphic look at the colours of Apple: https://68kmla.org/forums/uploads/monthly_03_2016/post-259-0-21697100-1459013587.jpeg

For a colourful overview of game consoles, see:

• Evan Amos, The Game Console: A Photographic History from Atari to Xbox, No Starch Press, 2018.