multiple colors for same line based on y value

hey nice job you're doing here i just want to reques politly for a simple feature to be added which is the ability to specify a different color for the same line based on the value of y like say i want my line to be green when its above 0 and red when its bellow
the effect can be achieved ib the current version buy using multiple line buts it gets a little messy removing and adding spots and calculating the intersections

No file or test is named. Start by reviewing the line-chart API and the current multiple-line workaround described in the issue; define how y-value thresholds and crossings should determine segment colors, then verify the behavior with line-chart examples or tests.

Written by the indexing model from the issue text.