For an unknown reason not mentioned about in any part of the wiki nor anywhere else, the Dust particles have become less defined in their ability to show color. 
Using translated commands between a world in 1.12.2 and 1.15.2, I show here, using the same color values, how the colors have become very dirtied and less capable. 
The colors in check are Pure White, and Bright Blue.
The bright ones are in 1.12.2.
Note: The darker shades were also completely possible in 1.12.2.
Thus, why has this changed, and why has no one spoken up about this???

To Reproduce White in 1.12: /particle reddust ~ ~ ~ 1 1 1 -0.01
To Reproduce White in 1.15: /particle dust 1 1 1 1 ^0 ^0 ^0 0 0 0 0 1 normal

To Reproduce Light Blue in 1.12: /particle reddust ~ ~ ~ 0 2 2 -0.01
To Reproduce Light Blue in 1.15: /particle dust 0 1 1 1 ^0 ^0 ^0 0 0 0 0 1 normal