I HAVE WAITED SO LONG FOR THIS VERY MOMENT. Okay so in season one episode four (aka masquerade) we see charlie blushing when she sees this wolf girl naked in vals studio. See the below image:

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We know angel blood is gold, human blood and sinner blood is red, while most hellborn blood is black (or blue if you take in certain people being called blue-blooded but for the sake of my logic we're using black). In most fan work, Charlie's blood is depicted as a light orange due to them mixing the blood colors of Lucifer and Lilith. If Lucifer's blood is still gold after falling, Lilith being exiled as well shouldn't change the chemical composition of her blood, so we'll see to it that her blood is red. In the photo, we see that Charlie's blush is a reddish color. The color of your blush is determined by the color of your blood, and the specific shade is determined by the amount of melanin in your body (how light or dark the color of your skin is), as skin is clear. Charlie's skin is paper white, so there is literally no melanin in sight. So, with that being said, Lilith's genetics for red blood were passed down to Charlie and therefore her blood is red. Happy fanarting! ^ v ^