What is the difference between parallel and layer nodes in DaVinci Resolve?

Both feed the same source image into multiple nodes, but parallel nodes mix all corrections equally while layer nodes give priority to the node connected to the bottom input of the Layer Mixer. Layer nodes also offer composite modes like Add and Soft Light; parallel nodes don't.

Should I use serial or parallel nodes for color grading?

Use serial nodes for primary corrections (exposure, contrast, balance) where each step should build on the previous one, and parallel nodes for secondary corrections (skin, sky, background) that each need a clean, stable feed of the same image.

What order should color grading nodes go in?

A reliable order is: color space transform in, exposure, contrast, balance, parallel secondaries, creative look or LUT, then color space transform out. Keep creative looks near the end so they don't break qualifiers downstream.

How many nodes should a color grade have?

As many as you have distinct ideas, and no more. One node should hold one labeled adjustment. Simple projects may need 3 to 5 nodes; complex commercial grades can run 10 to 15 or beyond.

Why did my qualifier stop working after I changed an earlier node?

Serial nodes build keys from the image the previous node outputs. Change that upstream node and the key is now reading a different image, so it breaks. Pull qualifiers in parallel nodes (or a Keyer node) so they always read a stable source.

Can I convert a parallel mixer into a layer mixer?

Yes. Right-click the mixer node and choose "Morph Into Layer Mixer" (or "Morph Into Parallel Mixer" to go the other way). You can also right-click either mixer to add more inputs.

Are Color page nodes the same as Fusion nodes?

No. Color page nodes are built for grading, with mixers designed around corrections and keys. Fusion nodes form a full compositing system for VFX, motion graphics, and 3D. The concepts rhyme, but the tools and workflows are different.