Pine script 在TradingView pine v4中执行指示器

我在这方面是新手，我正在做一些非常简单的事情，但我不知道为什么它不能编译

以下是脚本：

//@version=4
study("CrossOver", overlay = true)
sma_1 = sma (close, 4)
sma_2 = sma (close, 9)
sma_3 = sma (close, 18)

plot(sma_1, color = color.white)
plot(sma_2, color = color.red)
plot(sma_3, color = color.green)

longs = (sma_1 > sma_2) and (sma_2 > sma_3)
shorts = (sma_1 < sma_2) and (sma_2 < sma_3)
bgcolor(longs ? color.green : na)
bgcolor(shorts ? color.red : na)

---

您的脚本在此处编译良好：

line 10: Undeclared identifier `color.white`;
line 11: Undeclared identifier `color.red`;
line 12: Undeclared identifier `color.green`