you have a few options.
1. you can create a CMYK color fill and use process foils, but that will give you halftone screening (halftone dots) that can be altered by the dot type (shape) and LPI (dot size) in 'Menu>Halftone>Dot Type>LPI'
2. you can use solid spot color foils to create a "spectratone", Gerber's 2 color overprint to make a solid fill color. choose 'Spot Color Fill>Spectratone> and enter base layer color, and top layer color. to get a lime green the color ID software recommends lemon yellow on aqua, but depending on foils you have in stock, you may need to play with test prints of your different yellows on blues and see if any look close. you can now choose either the base or top layer and select printing percentages to screen back one or both to get a lighter print color, but you introduce the halftone screening (potential) problem again.
3. it may work out to be cheaper to buy a lime foil, or if any of the refill vendors sell 5yd/10yrd refills instead of a full 50yrd cartridge.
i use spectratone overprinting on a regular basis to create solid colors that i cannot get from just 1 foil. when using halftone screening and spectratones, i had to edit a halftone setting to allow dot on dot printing instead of the traditional rosette angled dot pattern. one of my customers needed a spectratone gradient and the rosette showed the 2 different colored halftone dots at different angles, instead of a single spectratone colored dots.
if anyone is interested in this step i can dig up my notes and do a tutorial.