Gizmo Dorks color changing filament is the best I have used yet. The colors are well saturated. This particular color is Blue and turns to white when warmed. This color appears close to cornflower blue. You could use it for novelty stress indicators, keychains, etc. It comes in 1KG size on a plastic spool.

https://amzn.to/2xTpKFW

Recommended Print Settings

Temperatures

• Hot End - 210 Celsius
• Bed - 60 Celsius

Speeds

• Print Speed - 50mm/s
• First Layer Speed - 30mm/s
• Perimeter Speed - 30mm/s
• Infill Speed - 60mm/s
• Cooling Fan Speed - 100%

Structure

• Perimeters - 2 or 0.8mm - 1mm
• Top and Bottom Layers - 4 to 5 or 1mm
• Infill - 15%

Retraction

• Distance - 0.8mm*
• Speed - 35mm*
• Z-Lift - 0.6mm

Bridging

• Bridge Flow - 85%
• Bridge Speed - 30mm/s
• Bridge Cooling - 100%

Physical

• Bed Adhesion - Glue Stick
• Nozzle Type - Brass (Standard)
• Enclosure - None