I just looked at Zoom's color plate and it does have a watermelon color to it but then it almost looks chartreuse. If you're using X2 colors try making a thin watermelon and then just dip a toothpick 1/4" into the chartreuse and stir that in. Its a nice color and shouldn't be too tough to match. Try the toothpick trick and see if it goes in the right direction. If it does but not quite, try another small dip of the chartreuse. Also, hold off on adding any glitter until you get the plastic color zoomed in. Glitter can play games with how you see a color.