Heat the annatto seeds in a dry skillet over medium-high heat until fragrant, about 2-3 minutes.

In a blender, combine the annatto seeds, orange juice, lime juice, vinegar, garlic, oregano, cumin, salt, and black pepper. Blend until smooth.

With the blender running, gradually pour in the vegetable oil until the marinade is emulsified and thickened.

Pour the marinade over your meat, fish, or vegetables in a large dish or resealable plastic bag. Marinate in the refrigerator for at least 2 hours, or up to 24 hours.

Remove the meat, fish, or vegetables from the marinade and discard the excess marinade. Cook as desired.