Amazon.com: Ohuhu Markers for Adult Coloring Books: 120 Colors Coloring Markers Dual Tips Fine & Brush Pens Water-Based Art Markers for Kids Adults Drawing Sketching Bullet Journal Non-bleeding - Maui - Black :
I got this swatch hex chart and it groups by similarity. Great for blending ranges. It was only $5 I think. You would really like it, I think : r/Ohuhu