Saria, color mixing is an art all of it's own, and am not very good at it. However if I experiment long enough I can come close to my reference. I can not tell you a formula on how to get this color, but can tell you it is not just one color. It appears they first laid down some hot pink and let it dry, then purple over it letting some hot ink show though. The white is most likely not white paint, but the white of the support (no paint in that spot) There is also the possibility that your reference was painting digitally .. not always and easy thing to copy with real paint. You should probably invest in a color wheel (plastic coated cardboard wheel available at any art/hobby store) This will help you understand what happens to a color if you mix it with another. One other thing that can be helpful is to get some 3x5 index cards and make some color cards. For instance, divide the card into several columns, pain one section with a base color, then add some white to that base and paint the next. Next add some black to the base and paint another. Mark each column with what you did .. something like B Purple +White +black. etc.
Then do another and this time add yellow and red to the purple.. If you do this with all your colors you will have a reference to go back to next time when you need to match something.
One other tip I can give you is to say a shadow is not black. A shadow is a darker value of the color on which the shadow falls. So if the shadow is on a blue wall you may want to add some dark red and a tiny touch of black to the blue to get the dark shadow color. Use black very sparingly. For instance the background of this painting is not black, it is 60%Raw Umber, 30% Purple and 10% black!
http://www.drawspace.com/forums/index.php?...i&img=35217I hope this was of some help, just keep experimenting, it is just paint.. you can't hurt anything, just have fun!