By adjusting the appender color we set ourselves up for a situation where the contrast with the background is so low that it won't be visible and hampers usability.

I wonder if instead, we should give it a white or black background and border and keep it the opposite color to make it always visible. Something like this?

I added the design labels as this might be an approach that impacts future blocks as well.

Testing with twenty-twenty I see how that the appender looks, pretty similar how @obenland mentioned before:

I like the idea of a white background for it, means it's more consistent with expected appenders. My only wonder is other appenders on that page might not have it.

This is an example.

We do seem to colour one and not the other so there might be history there we can fall on:

I like the idea of a white background for it, means it's more consistent with expected appenders. My only wonder is other appenders on that page might not have it.

Right, consistency is a valid point. Coloring the appender with the text color (first approach on this PR) maybe make more sense?

Right, consistency is a valid point. Coloring the appender with the text color (first approach on this PR) maybe make more sense?

This feels like maybe best yes.

The one issue with using text color is that it might still have low contrast if the user selects a low contrast text color. Having said that since it's a user selection I think that seems okay.

The one issue with using text color is that it might still have low contrast if the user selects a low contrast text color. Having said that since it's a user selection I think that seems okay.

Yes, any control should be accessible beyond the user customization. Maybe, by mistake, the user sets a wrong combination and stop seeing the appender button. Anyway, this possibility can happen in the current implementation.

Also, we should keep in mind the probably the styles will change soon according to changes suggested here #19681

I wonder if instead, we should give it a white or black background and border and keep it the opposite color to make it always visible.

I think this is the best solution. This is how the inserter works normally when using a theme with a dark background, always showing a white background behind the + icon.

Since the appender now has a black background, can we close this one?

Yes.