QlikView has a color function called colormix to return an ARGB value from a two color gradient. There are two versions, Colormix1 and Colormix2 depending on the range of values. Colormix1 is for a range between 0 and 1, Colormix2 is based on values between -1 and 1. So if your values are percentages, then using Colormix1 with red as ColorZero and green as ColorOne should work for you.
See help for more details.