The colour of a directions layer in Google My Maps is always blue.
You cannot change it in that layer, despite it being a long standing feature request: [WaybackSave/Archive] how can i use a different line color on each layer for my bike routes? – Google Maps Community
If you are creating Directions layers on My Maps it is not possible to change the color of the lines. It is a often requested feature but so far Google has not implemented it.
There is however w workaround answered in [Wayback/Archive] mymaps – How to change the road color in Google My Maps – Stack Overflow (thanks [Wayback/Archive] Ben for asking and [Wayback/Archive] Richard de Ree for answering):
[