Why is the combination of Blue/Green/Yellow/Red squares or letters such a popular scheme used in many logos of tech companies? The popular examples being the Windows Flag icon, Google logo and the Google Chrome logo, CMake logo (triangle), Ebay logo etc..
If you know of the opponent-process theory, you will know that there are 6 'special' colours: Black, white, red, green, yellow and blue.
Although the receptor cones in the eye are sensitive to Red, Green, and Blue, prior to processing the brain encodes the information using 3 channels:
These 6 colours are thus termed unique hues as each represents an extreme in one of of the 3 channels.
When more than one colour is needed, using unique hues allows more colours to be used and easily distinguished. As using them reduces the need for the designer to consider various aspects of colour theory, such as luminance or chrominance contrast.
These 6 colours are also great for learnability - they are so distinguished from one another that it makes information coding easier compared to using non-unique hues.
Reference: Visual Thinking for Design (Ware, 2008); Chapter 4 (Colors).
I do not think visual theory and wavelengths are the primary reasons for this.
I also think it has something of the playful-childish-element to it.
Yes, tech companies often use primary colours, that we otherwise find in logos for childrens shops etc. I doubt you will find a non-child-related company from before 1995 that uses primary colours that liberally.
Tech created an entirely new visual "we are geeks but we are fun, and we have wacky company names too" culture. I also seriously doubt you will find a builder, solicitor, hairdresser, carpenter, butcher, supermarket, used car sales etc with multiple, primary colours a lá Google chrome. It is traditionally not "confidence-building" in other fields.