When adding custom colours, by double clicking on the colour field in the Attributes section, they are not saved to the Colour pop-up screen for future re-use.
At this stage, that would be a feature request and not a bug.
The feature to add a custom colour is already build in as per attached file 1. The bug is that this feature's "Add to custom colours" does not save the custom colour for later reuse.
Their implementation and the reason for pulling up a Color Picker Dialog box is in direct response to setting a color attribute value for a component (ie: .bco/,pco). From that aspect, the color picker has done its task.
The fact that they have used a color picker dialog box that also includes spots that COULD be also used to house and store previously chosen colors - was never been implemented as such, ever. There is zero code in the Nextion Editor to attempt to capture the chosen color values. Therefore, it is not a bug, it is a possible future feature that remains yet unimplemented. To be a bug it has to be malfunctioning code, so where zero code has ever existed it is not a bug.
It would make a good candidate for a feature request.
Saving the color in custom colors has been as will be an ongoing feature request.
As this is not a bug, this will now be marked as solved.