In Spine, you cannot change the attachment color in animate mode. Attachment colors are set in setup mode and cannot be keyed in animations. Instead, you can animate the slot color, which affects the appearance of the attachment during animations. This is because the slot color can be keyed and changed over time, allowing for dynamic color changes in animations.

Spinebot is correct

warmanw You cannot change the color of multiple attachments in an animation, only slot color and alpha can be keyed.
https://esotericsoftware.com/spine-attachments#Color
https://esotericsoftware.com/spine-keys#Slot-color

warmanw Hmmm, I am actually not sure if this is a bug or not. The condition for enabling attachment color changes even in animate mode is to select multiple attachments of different types, but I think this is allowed considering the possibility that the selected attachments may include attachments such as clipping, bounding box, path attachments, etc. whose colors are not actually related to the animation.
It would be possible to disable attachment color changes when the current selection includes region or mesh attachments, but I personally think it would be better to leave the current behavior as it is, as I think it would add more work in some cases.
(I would have thought that if changing the attachment color was only possible when certain steps were taken, then it should be fixed as a bug, but as far as I have tested, the behavior seems to be consistent, as you can always change the color when selecting different types of attachments at the same time, regardless of what the previous or subsequent operation was.)

Waiting for Nate to say, "It's not a bug, it's a feature". ¯\(ツ)/¯

warmanw Clipping and bounding box attachments can be changed the attachment color within the animate mode. While checking, I noticed that for some reason the path attachment cannot change color in animate mode when it is selected singly, so perhaps this should be fixed.
As for the region and mesh attachment color, I think it makes sense not to allow them to be changed in animate mode. In fact, some users have been confused in the past about how to animate colors because the attachment color and slot color are similar. To avoid such confusion, it would be better to only allow slot colors that can be keyed to be changed in animate mode.

For reference, how often in your workflow do you want to change the region or mesh attachment color in animate mode?

We've consistently found typical noob users, not you advanced guys, get tripped up by changing things in animate mode that cannot be keyed. What we want to do is prevent it all by default, even more than we already do: no changing weights, colors, etc in animate mode. Then we'll have a setting that enables changing all the things in animate mode. It's better for the noobs, and better for you guys!

For now I think we can leave multi-select attachment color changing, as it's somewhat unlikely that noobs trip over it.