Based on your description of wanting a modern yet retro feel for a second-hand app, I’ve created a color palette that complements your background gradient of #3f0f27 to #fca182 . This palette captures the nostalgic vibe while incorporating modern elements.

 <Retro Modern>
1. Vintage Rose - 
                            
                            #D54E7A
                         - A soft, muted pink that evokes feelings of nostalgia and warmth, perfect for a retro theme.
2. Teal Blue - 
                            
                            #008080
                         - A calm and inviting teal that adds a modern twist, providing a fresh contrast to the warmer tones.
3. Mustard Yellow - 
                            
                            #E1B000
                         - A bold mustard that brings energy and brightness, reminiscent of retro designs while still feeling contemporary.
4. Deep Plum - 
                            
                            #7A2C4C
                         - A rich, deep purple that adds depth and sophistication, enhancing the retro feel.
5. Cream - 
                            
                            #FFF5E1
                         - A soft, creamy hue that serves as a neutral base, balancing the brighter colors and maintaining a modern touch.

This color palette combines warm and inviting colors with a touch of modernity while staying true to a retro aesthetic.

How do these colors resonate with your vision for the app? Would you like to see variations or additional colors?