Interaction Lines as a Color Gradient (function: plotweb) (package: bipartite)

Any ideas on how to code the interaction lines (currently lavenderblush4) as a color gradient from the lower to upper boxes? I’m trying to make it go from green/red to whatever color I choose for the black boxes.

plotweb(Crep_spe, labsize = 2, text.rot=90, col.interaction = "lavenderblush4", col.high = "black",col.low= c("olivedrab","indianred3","indianred3", "indianred3","indianred3","olivedrab","indianred3","olivedrab","indianred3","indianred3", "indianred3","olivedrab", "indianred3", "olivedrab","olivedrab","indianred3","olivedrab","indianred3","indianred3","indianred3","indianred3","olivedrab","indianred3","indianred3","olivedrab","indianred3","indianred3","indianred3","indianred3","indianred3","indianred3","olivedrab","olivedrab","indianred3","olivedrab","olivedrab","olivedrab","indianred3","indianred3","olivedrab","olivedrab"),y.lim = c(-0.9,2.7), high.lab.dis=0.02, low.lab.dis=0.02, arrow = "up.center"