[sime2009]

Using bright colours for bold made sense years ago when we had much lower resolution displays. The fonts used back then were pixel based and tiny. (Think 8x8 or 8x7) It often wasn't possible to be make a bold version of a pixel font that size. You just can't do fat bold lines and not end up with a blob.

[JdeBP]

That argument flounders on the fact that in the pre-VGA (more strictly pre-CGA) world boldface and blink did not change colours, either. There was a whole world of monochrome video terminals. And, furthermore, the fonts during the heyday of the home computer revolution were boldface in several cases, including the BBC Micro's graphics mode character set, even though they were smaller than 8 by 8.

* https://damieng.com/blog/2011/02/20/typography-in-8-bits-sys...