Previously, values ​​above 1 would still affect the colors of particles like "dust".
For example, very large values ​​could be used to create colors that were not possible with the normal color settings.
The screenshot showing the yellow particles was taken in 1.21.1.

Here is an example command:

/particle minecraft:dust{color:[100000000.0,100000000.0,1.0],scale:1} ~ ~ ~ 1 1 1 0 1000

However, in 1.21.2-PreRelease 1, any value above 1 seems to be treated as 1.
The screenshot showing the white particles was taken using the same command in the pre-release.