It is an RSI indicator with 3 lines (or 4 if you enable the original RSI in settings):
The lime is calculated from high
The fuchsia is calculated from low
The orange one is calcuated form both high and low, by calculating RSI's up from high and down from low
You can also select different moving averages for RSI calculation. (The default is the original RMA)
This indicator is useful for e.g. to filter out original RSI's false signals by waiting both low and high lines to confirm. Or you can use it as an earlier exit indicator. Please write a comment if you find another usage of it.