Option to enable/disable Greasepencil Vertex Color on existing strokes

There should be a switch to disable/enable vertex paint colours on existing strokes, either under object properties or layer properties.

That would solve the problem brought up in a couple of questions on blender stack exchange ( here and here ).
What happens is that the user switches view to solid and inadvertently enables Vertex Color mode. Because of the solid view, the vertex colour doesn't show, so the user goes about colouring stuff, creating multiples materials, every time selecting an appropriate colour and seeing that colour applied on their drawing.
When comes render time, everything turns one colour, the one that happened to be selected in Vertex Color mode.
So one could think it's a user mistake, and it is, but Blender never gave any feedback to the user about what was happening. More importantly, the real nightmare is that there isn't any way to go back to the materials even tho the info is there (and plainfully visible in solid view), the vertex paint overrides everything. The only option is to replace the vertex colour for every single strokes of every single frame, which can take close to forever depending on the drawing's complexity.

A checkbox would resolve all of that.