Yes. The Game Boy Light (Japan-only, 1998) plays all original Game Boy and Game Boy Color cartridges regardless of region—there is no region locking on Game Boy/Color hardware.
The label on the back reads "GAME BOY LIGHT" and "Made in Japan." No region code sticker exists because none is needed.
Modern flash carts (EZ-Flash Jr., EverDrive-GB) let you load ROMs from an SD card and work perfectly on Game Boy Light.
Bottom line: Your Japanese Game Boy Light will play US/EU Game Boy and Game Boy Color games natively.