Here’s a color palette that transitions from the dull purple to the deep blue-green, inspired by the iridescence of a beetle’s shell:

 <Iridescent Beetle Shell>
1. Dull Purple - 
                            
                            #403353
                         - A muted, deep purple that serves as the starting point of the palette.
2. Dusky Lavender - 
                            
                            #5B4B73
                         - A soft transition color, blending hints of lavender with the dull purple.
3. Twilight Blue - 
                            
                            #3A4B70
                         - A cool, muted blue that bridges the gap between purple and green.
4. Deep Teal - 
                            
                            #2C4A4B
                         - A rich teal that introduces green tones while maintaining depth.
5. Deep Blue-Green - 
                            
                            #063931
                         - A dark, deep blue-green that concludes the palette with intensity.

This palette captures the essence of transitioning colors, maintaining a balance between the dull purple and deep blue-green, while evoking a feeling of iridescence.

Would you like to explore specific design applications for this palette or need adjustments to the colors?