The histogram displayed is the difference between a shorter time period FXI - Instant Trendline and one of a longer length. If the histogram is above zero, then the shorter period value is above the longer period value. Visa versa for below zero. If the bar is
green, then the value is above the previous bars' value. If it bar is
red, then the value is below the previous bars' value.
The FXI - Velocity Rainbow indicator displays directional velocity of the price movement of the instrument across three timeframes. By taking the difference between a short and long time period FXI -Instant Trendline, we can see which direction the price move is going and how strong a move it is making. And by viewing this difference across three time frames at the same time we can see whether the price move is supported or contradicted by the upper time frames with just one glance.
The red line shows the Instant Velocity of the current time frame while the green and blue lines show the Instant Velocity of the two upper time frames. In this way you can see whether the lower time frames' price moves are accelorating in the same direction or against the direction of the upper time frames' direction. Such information is helpful in order to see if we are trading with or against the trend and to adjust our actions accordingly.