Call your local Hwy Patrol or DMV.
Usually amber or white is fine, its the blue or white-ish blue crap that is illegal.
I googled Minnesota DMV for you...
LINK
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Prohibited Lights taken from the MINNESOTA DEPARTMENT OF PUBLIC SAFETY, DVS Drivers Manual
Blue lights, flashing lights, and strobe lamps serve special purposes. They are not for use by non-authorized vehicles.
Only snowplows, other road maintenance equipment, and authorized emergency vehicles may be equipped with blue lights. Only authorized emergency vehicles, school buses, road maintenance equipment, tow trucks, service vehicles, and farm equipment may be equipped with flashing lights. Only school buses, snow removal equipment, and rural mail carrier vehicles may be equipped with strobe lamps.
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...so, it looks like you will be fine with white.
btw wrong forum, moved to G/D.