The bug
When coloring a beacon beam with colored glass, the color will be correctly applied only if you place the colored glass directly on top of the beacon. If you place the colored glass a few blocks above the beacon, the beacon beam will act as if there were white glass blocks between that glass block and the beacon.
How to reproduce
Build a beacon
Place a red glass block on top of it
→ ✔ The beacon beam is completely redPlace another red glass block on top of the first one
Break the previous red glass block
→ ❌ The beacon beam is now pink-ish
Related issues
is duplicated by
relates to
Attachments
Comments

Can't reproduce. Beacons in 1.14-pre2 appear like they do in 1.13.2. Are you sure you don't have any other resource packs enabled that are affecting the colors?

Really? Odd. I always go with the default textures when testing. I tried optimizing then re-upgrading from the source. Same problem. I upgraded from this home base location this time and status effects showed up briefly then went away.
[media]

Re-upgraded from 1.13.2 (not Pre-Release 3).

I can reproduce in 1.14 release, but for more info: it only seems to happen if there's a gap between the beacon and the first stained glass block.
If the stained glass is right up against the beacon, it works as before, setting the colour of the beam.
But if there's an air gap, seems like now the beacon beam is treated like it's been coloured white, and gets averaged with the the first glass block it comes across, giving this much paler colour.
[media]
In 1.13 both of these beams would be solid red.

This has happened to me as well.
When a brown glass block isn't directly above the beacon, the beam looks light-gray