<Black Elegance>
1. Onyx - 
                            
                            #353839
                         - A deep, rich black that provides a strong foundation.
2. Charcoal - 
                            
                            #4B4B4D
                         - A slightly softer black with gray undertones, adding depth.
3. Jet - 
                            
                            #343A40
                         - A dark gray-black that offers a modern touch.
4. Raven - 
                            
                            #2C2C2E
                         - A pure black with a hint of warmth, perfect for accents.
5. Midnight - 
                            
                            #1C1C1E
                         - An almost black with subtle blue undertones, giving a sophisticated feel.

This color palette, “Black Elegance,” combines various shades of black and dark gray to create a sophisticated and modern look, ideal for a technical diagram like a TCP header format illustration. The subtle variations in shade help to distinguish different elements while maintaining a cohesive and elegant aesthetic.

Would you like to explore any specific accent colors to highlight certain parts of the diagram? Or are you looking for a different theme altogether?