If your ordering prepainted parts, you better make sure you know the correct paint code. Finding the paint code is easy if you know where to look. It is always listed on the inside sticker on the drivers door (See Pic). You are looking for a code to tell you the color. Here are a list of codes that were used on the mustangs.
1999-2004 Mustang Paint Codes:

• Dark Shadow Gray Pri Pearl - CX
• Competition Orange - CY
• Colorado Red - D3
• Screaming Yellow - D6
• Merlot Pearl - FX
• Redfire Pearl Metallic - G2
• Mystichrome Metallic not available - G6
• Azure Blue Pearl Metallic - L5
• Sonic Blue Pearl Metallic - SN
• Black Ebony - UA
• Silver Metallic - YN
• Oxford White - Z1

2005-2009 Mustang Paint Codes:

• Colorado Red - D3
• Screaming Yellow - D6
• Redfire Pearl Metallic - G2
• Vista Blue Metallic - G9
• High Performance White - HP
• Lime Gold Metallic - P1
• Windveil Blue Metallic - P3
• Tungsten Gray Metallic - T8
• Satin Silver Pearl Metallic - TL
• Mineral Gray Pri Metallic - TK
• Black Ebony - UA

2010 Mustang Paint Codes:

• Grabber Blue - CI
• Torch Red - D3
• Sunset Gold - GQ
• Performance White - HP
• Kona Blue - L6
• Red Candy - U6
• Black - UA
• Brilliant Silver - UI
• Sterling Gray - UJ

2011-2012 Mustang Paint Code:

• Grabber Blue - CI
• Kona Blue - L6
• Yellow Blaze - NQ
• Sun Set Gold - GQ
• Torch Red - D3
• Race Red - PQ
• Red Candy - U6
• Laza Red - UZ
• Black - UA
• Sterling Gray- UJ
• Competition Orange - CY
• Performance White - HP
• Brilliant Silver Metallic - UI
• Ingot Silver Metallic - UX