This achievement unlocks after the final level in the chapter is completed.
Here's the guide I used from Scottii's YouTube channel, give him a like to show thanks.
Chromagun: Chapter 5 Level 1Chromagun: Chapter 5 Level 2Chromagun: Chapter 5 Level 3Chromagun: Chapter 5 Level 4Chromagun: Chapter 5 Level 5Chromagun: Chapter 5 Level 6Chromagun: Chapter 5 Level 7