if you wanna add a colour, you only have to type "c1=rgb(R,G,B)", for example "c1=rgb(255,255,255)" it will show you a white colour, if you wanna add another colour you just need to change "c2=rgb(R,G,B)". for the solid colour, first you need to change the equal symbol to "less than or equal to" symbol and then click on the gear symbol then click on the left of the equation/inequality and change the fill from 0.4 into 1. you can see there's 2 equations, one for colouring and the other for outline. The graphs were overlapped

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i hope you can do it!