Welcome to the Quilting Board!

My suggestion is to go somewhere other than that quilt shop. You need to go to a shop where your ideas will be listened to and then several ideas suggested that would work with the ideas you already have. That's why we go to a quilt shop! I wish you luck and success on this! And blessings to your son for serving.
"A woman is like a tea bag-you can't tell how strong she is until you put her in hot water." Eleanor Roosevelt
I am sure that it will be loved by your son. I don't think those are "girly colors" as they are the colors chosen by many of the armed forces. I just finished one for my grandson who is getting married this month. Although it is busy, it contains many of the colors you listed. My first quilt top since my accident in april! Good luck with the quilt and be sure to post the pictures when you have it done. I know it will be fantastic.
I'd tone the whole thing down, go away from black black and use a mottled dark charcoal in it's place. I'd use deep, rich masculine burgundy, forest green, warm gold along with the dark charcoal and then I'd let it fly with the shield...clean bright true to image colors. Let' see If I can upload this picture which has the charcoal I'm talking about... sorry, floundering around looking for an upload image link. I"ll post pic once I find the link.
Blues an browns would be good. you might ad in a bit of deep gold color, not yellow.
A friend is someone who knows all about you and loves you anyway.
I think the greys, blues, reds, bright golds and blacks will be perfect for this quilt! It won't be too feminine, and I think tone on tones, batiks or marbles qould be lovely! Please let us know what you decide!