Colorize points by height gradient.

Arguments

• positions — Float32Array [x0, y0, z0, x1, y1, z1, ...]
• min_z — Minimum Z value for gradient start
• max_z — Maximum Z value for gradient end
• low_color — Float32Array [r, g, b] (0-255) for min Z
• high_color — Float32Array [r, g, b] (0-255) for max Z

Returns

Float32Array RGBA [r0, g0, b0, a0, ...] (0.0-1.0).