Filter -> Noise
Do it on an empty layer, then use one of the layer blending modes (and layer transparency) to get what you want.
Random RGB noise will work, just desaturate it to get grays again.
This isn't even true either. Sun named Java "Java" because reasons (which were probably coffee related) and then spent a few million dollars marketing it.
JavaScript on the other hand was being developed independently, saw the huge advertising Sun was doing for Java and said, "We need to name it Java-something so that we can piggy back off their advertising."
Slight correction, based on my understanding:
updatePostPlacement - called immediately after the player places the block in order to check to see if any state change should occur based on neighbors. (Eg. placing concrete powder next to existing water)
neighborChanged / onNeighborChange - called when a neighbor changes state in order to see if any state change is necessary. (Eg. water flows into the space next to concrete powder)
observedNeighborChange - specific to the observer block, but similar to neighborChanged. I haven't messed with it.
To explain, we can't support old versions forever as doing so requires people who know the version and as new versions come out, people not using the old version forget how to work with it.
You can see how I handled it in 1.14:
https://github.com/Draco18s/ReasonableRealism/blob/1.14.4/src/main/java/com/draco18s/hardlib/api/internal/ModItemGroup.java
https://github.com/Draco18s/ReasonableRealism/blob/1.14.4/src/main/java/com/draco18s/industry/ExpandedIndustry.java#L59
(IItemProvider is approximately equal to a Supplier<ItemStack>, pretty sure the latter replaced the former, but the end result is pretty much the same)
You mean a red underline? Yes, it would, but just because it turns red doesn't tell us what your IDE is saying is wrong. All that is is "there is an error here."
What error?
Your message is coming from your mod, from no where, you don't need a website to find a player's UUID, you either get the UUID from an entity itself or don't need a real UUID at all, in which case you need a dummy UUID, which diesieben07 already told you how to get.