Ersoy relative Strength Index

study(title="Ersoy/relative Strength Index", shorttitle="RSI")
src = close, len = input(14, minval=1, title="Length")
c= src[1]<src ? lime:red
up = rma(max(change(src), 0), len)
down = rma(-min(change(src), 0), len)
rsi = down == 0 ? 100 : up == 0 ? 0 : 100 - (100 / (1 + up / down))
plot(rsi, color=black)
band1 = hline(70,color=red,linestyle=solid,linewidth=2)
band0 = hline(30,color=lime,linestyle=solid,linewidth=2)
fill(band1, band0, color=aqua , transp=90)
plot(50,color=c)
bgcolor(up>down ? lime:red,transp=20)