I made a multi-color “neon” sign using LED strips

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Outdoor Silicone Blue Yellow Red Green Color Strip Light

This ultra concentrated RGB LED strip crams in 332 tiny individually addressable LEDs per metre, with a narrow silicon diffuser strip over the top for a cool neon effect. It's sold in 0.5m and 1m strips, with a connector at both ends so you you can easily chain multiple strips together. There's also extra power/ground wires at both ends of each strip so you can inject additional power if you're running long lengths of the stuff.

Ultra-dense RGB Micro Led Strip (aka NeoPixel, WS2812, SK6812) 0.5m

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Govee RGBIC Neon LED Strip Lights 3M, DIY Shape, Segmentable

Direct Install 6mm 10mm LED Strip RGB Custom Neon Sign I - China

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Premium LED Strip Lights & LED Neon Flex - UK LED Lights

Govee RGBIC Neon LED Strip Lights 3M, DIY Shape, Segmentable