The ColecoVision can output RGB, composite and S-Video with a modification. Stock consoles only output RF video. Please read on for more information.
Like many other consoles of the time, the ColecoVision only offered RF A/V output, with no other stock choice. For a long time, the only modifications available were composite and S-Video, but more than thirty years after the console’s release, an RGB mod was created! Check the links on the right for DIY kits:
RGB / VGA Mod:
The latest Colecovision RGB kit is from Nicholas Piegdon aka Falonn. This kit is meant to work with any console that’s based on the TMS9928A and TMS9929A graphics chips and is designed to work around their shortcomings. Here’s a page with all the info you’ll need: https://tms-rgb.com/
If you’d like to purchase pre-made boards, Mobius Strip Tech is currently selling them: https://mobiusstriptechnologies.com/product/colecovision-rgb-board/
Dan aka Citrus3000psi also signed a Colecovision board that’s available on OSHPark for anyone to download. This kit is easy to install, but requires an oscilloscope to properly calibrate.
VGA DIY Kit: There’s a board called the “F18A” that replaces the video encoder with a custom board that outputs 480p VGA: http://codehackcreate.com/store#!/F18A-V1-8-Video-Board/p/14022176/category=0
As an FYI, the RGB and VGA mods are not compatible with the Atari 2600 adapter, since it bypasses the internal circuitry. There’s an Atari 2600 RGB mod now available though and the 2600 is also supported in the Analog NT Mini.
A complete FPGA re-creation of the Coleco was made, called the Colelctorvision that can play original cartridges and use original controllers. It outputs 480p vai HDMI and might be a good choice for people who want a look that’s reminiscent of the original console, without the modding required to get an original console looking good on a flat-panel TV: https://collectorvision.com/shop/colecovision/collectorvision-phoenix/
The MiSTer project has an Colecovision core that works really well! Please check out the MiSTer page for more info, but if you don’t mind some DIY setup, the MiSTer is an extremely cost-effective way of experiencing many classic game consoles: https://www.retrorgb.com/mister.html
If you’d like info on mods for other systems, head to the Getting RGB From Each System page or check out the main page for more retro-awesomeness.