In C2 the SetColor Effect has 3 parameters R, G and B. In C3 it has only 1 parameter. You have to use the rgb-command with the same 3 parameters as values.
In C2 it looks like that:
Parameter 0 has the value: 255 - (smiley.HP / smiley.MaxHP * 255) that is your R(ed) value.
Parameter 1 has the value: smiley.HP / smiley.MaxHP * 150 that is your G(reen) value.
Parameter 2 has the value: 0 You don't set any B(lue) value.
In C3 there is only one parameter for SetColor but that expects a rgb-value rgb(R,G,B). So you have to set the parameters from C2 as values in the rgb-command:
rgb (255 - (smiley.HP / smiley.MaxHP * 255), smiley.HP / smiley.MaxHP * 150, 0)
In C3 it looks now like this:
The example as c3p: