Red "missing nodes" when you open a workflow
A node pack is missing or too old. Here is what to install or update.
Pixaroma nodes (their names end in "Pixaroma")
The workflow uses a newer node than you have. Update, then restart ComfyUI: with Easy-Install or with git pull. Then press Ctrl Shift R in the browser.
Other nodes
Pixaroma workflows list the packs they need in their Download Models button; other workflows in a note. To install one: Manager, Install Missing Custom Nodes, Install next to the pack, then Select (latest). When it is done, press Restart, confirm, and press Ctrl Shift R in the browser.
Some packs need extra files. If one stays red after the restart, read the red text in the black console window: it names what is missing.
Updated and still red?
For a Pixaroma node: click the ? in the top bar and check that your version really went up (the bottom right corner of the Pixaroma Help window). It did not go up, or it did and the node is still red? Reinstall cleanly, then press Ctrl Shift R in the browser.