When you import pins in KML format the original color from the KML file will be set to default red color.
You can use text editor to adjust the color for all pins in the file. When you open the KML file in text editor, you'll see the text with the info about your pins.
The text below contains the info about one bookmark.
placemark-red shows the color of the pin.
You can find and replace “red" with the any of 8 colors available in the app (green, red, yellow, blue, purple, pink, orange, brown) for all pins in the file. Then, you can save changes and import the KML file back to MAPS.ME.