Show HN: Smart Color Replacer with HSV tolerance and edge snapping

After getting tired of Photoshop's magic wand failing on product photos, I built this color replacer with features most online tools don't have:

• HSV tolerance (not RGB) - Catches all blues regardless of lighting while ignoring whites/grays that RGB tools pick up

• Magnetic lasso-style edge snapping - Uses Sobel edge detection so polygon vertices snap to object boundaries automatically. Green vertices = snapped, yellow = free placement

• Multiple independent color pairs - Replace 5 different shades with tight tolerances instead of cranking up one slider and getting color bleed

• Preserve shading toggle - Change a pink shirt to blue while keeping all fabric folds, shadows, and highlights intact

• Editable polygons - Drag vertices after closing, undo points, hide overlay while keeping selection active

• Remove colors → transparency - Perfect for background removal when you know the bg color

Problem with RGB: White (255,255,255) is mathematically close to Light Pink (255,182,193). HSV separates Hue from Saturation/Value, so you can target "all pinks" while excluding "anything low-saturation" (whites/grays).

Free, browser-based, no account needed. Built for e-commerce product recoloring and design mockups where simple flood-fill tools fail.