You have violet paint what color must you add to make it a dark red?
I'm sorry, it can not be done... Tintable paints come in several
tint bases, the paler the colour the more white pigment is in the
original tint base. Violet is a pale colour and therefore will have
been mixed in a pastel tint base containing a large amount of white
pigment. Dark red needs to be mixed in a dark of red base,
depending on how dark you want it. No amount of red colourant will
bring violet to the range of colour you desire.