To politely decline attending a wedding due to not having an appropriate gown that matches their color motif, you can use the following example message:
Subject: Regrets for the Wedding Invitation
Dear [Friend's Name],
I hope this message finds you well. I want to express my heartfelt gratitude for inviting me to be a part of your special day. It truly means a lot to me that you thought of including me in your wedding celebration.
However, after much consideration, I regretfully must inform you that I won't be able to attend the wedding. The reason behind this decision is that I currently do not have an appropriate gown that matches your beautiful color motif. I believe that your wedding day should be a perfect representation of your vision, and I wouldn't want to stand out or detract from the overall theme you have carefully chosen.
Please know that it was not an easy decision for me to make, and I genuinely wish I could be there to share in your joy and happiness. I assure you that my absence in no way reflects how much I care about you and your partner.
I promise to celebrate with you in spirit from afar, and I eagerly await the opportunity to catch up with you after your wedding to hear all about the magical day you'll have.
Wishing you nothing but love, happiness, and a lifetime of cherished memories together.
Warmest regards,
[Your Name]