Way too much drama about a deskmat design colourway. The thematic overlap is clearly coincidental due to the recent Day of the Dead date.
Whether or not the new colourway matches GMK Mictlán occurred deliberately or coincidentally doesn't matter.
As long as the artwork is original, the deskmat designer can do it in whatever colourway variations they wish, even if it happens to complement another set. They do not need the keycap set designer's permission.
If I release rose gold+black+white or red+blue colourway of a deskmat design would I need to speak to Olivia (GMK Olivia) and MiTo (GMK Laser) for their permission?
Vheissu (designer behind GMK Mictlán) has already commented stating their position that they have their own deskmat designs in the works, and OP (Ferry from PhangKey) has released a statement that they have already reached out and communicated with Vheissu. So consider the matter settled.
I like that OP took feedback from the community to improve the product proposed before going to GB (validating the purpose of this forum).
I for one, also appreciate that there's more deskmat options available to match a great looking set.
I will also keeping an eye seeing what the GMK Mictlán official deskmat designs look, to see how another artist executes the theme (which I have a soft spot for due to the film Coco).