The new indicator is given below, which will plot 2 lines, x1 & x2. x1 is above 0, and, x2 is below 0. Select these separately, and, change style to histogram and required color for each. Hope this is helpful.
SMI (13,25,2)
q:=Input("Lookback Periods?",1,1000,13);
r:=Input("First EMA Periods?",1,100,25);
sm:=Input("Second EMA Periods?",1,100,2);
x:=100 *
(Mov(Mov(C-(0.5*(HHV(H,q)+LLV(L,q))),r,E),sm,E) /
(0.5*Mov(Mov(HHV(H,q)-LLV(L,q),r,E),sm,E)));
x1:=if(x >= 0, x, 0);
x2:=if(x <= 0, x, 0);
x1;
x2;