This is, no doubt, aimed at rhyming with the expression "donner carte blanche" and the verb "donner", which is remarkable for the lack of specificity it shows, for its common place connotations, has been chosen expressly with that in mind; normally, a verbe such as "fournir", or "remettre", or an expression such as "joindre à leurs explications une carte coloriée" would have been more proper than this word connoting essentially the idea of a gift or nothing in particular (as when handing sth to someone you say "donner qqc à qqn").The idea of colored chart is by the way, overplayed, the chart is of a uniform light blue colour (shown below).

I've never heard or read any figurative expression similar to "laisser carte blanche" using the term "carte colorée".
Nevertheless, the idea is very probably gratuitous, as is all the hulaballoo about Trump being the only politician on the planet having to rely on charts and maps for acquiring and retaining some knowledge about complex global and regional situations. There is no context for the Japanese delegating decision power to American administration in matters of trade: all decisions in that domain are the product of bilateral arrangements or unilateral impositions, except possibly on the level of very limited facets of the business, but that's out of the question here.