PurpleHeart (bright Purple), Padauk (bright Orange) and Bloodwood (bright to Dark Red) will all darken in time if exposed to UV rays from the sun. These Crosses should not be in direct sunlight or they will darken quickly to a brownish color.
Good news though. They are NOT permanently damaged and can be rejuvenated quickly by sanding them, then letting them react with the air (oxidize), and they will soon take on a bright Purple, Orange or Red color again.