Aegisub

水平漸層色
{\pos($x,$y)\clip(!_G.interpolate((j-1)/maxj,$lleft,$lright)!,$ltop,!_G.interpolate(j/maxj,$lleft,$lright)!,$lbottom)\1c!_G.interpolate_color(j/maxj,"&HFFFFFF&","&HFF0000&")!}
垂直漸層色
{\pos($x,$y)\clip($lleft,!_G.interpolate((j-1)/maxj,$ltop,$lbottom)!,$lright,!_G.interpolate(j/maxj,$ltop,$lbottom)!)\1c!_G.interpolate_color(j/maxj,"&HFFFFFF&","&HFF0000&")!}

....