Item sent a different colour - dispute

[ShortyShortLegs]

Hi, I ordered a silvery holographic creasured texture backpack for my daughter for college, a bum bag was sent in error.
I told the seller (a business) and they sent out the correct size bag now, but the wrong colour. The smaller bag was the correct colour so I have a comparison in my hands! The seller is insisting the bag is the correct colour...it is not, it is pink holographic, smooth not textured.
Seller now wants me to return the backpack, then will resend a replacement in a different colour which he says is closer to the original. He has said he will refund me the postage costswhich is nice of him, but it is extra hassle going to post office etc. and I don't know if the next backpack will even be the actual colour daughter wants...
I wouldn't be so fussy normally but daughter really wants a silver holographic one, it has cost £30 and it is her own money.
I've added pics....(1st) the backpack top, bum bag bottom (2nd) the screenshot of what seller says we have and is offering to send (3rd) sellers page - we ordered the first on bottom row, think we actually have the fourth on that row.
What do you all think? Is it pink??

It looks like a silvery pink to me (sorry).

I'm not sure what you want here. Well I am, but not sure what advice you're looking for?

The seller has offered to replace at his/her own cost. If you're not satisfied with a resolution via that method then the only other option is to send it back for a full refund?

I don't understand the problem. He's going to replace it?

What I want is a silver holographic backpack like the one in the listing, not a pinky holographic one or a flat silver one that isn't holographic....
I can't seem to get him to understand that what has been sent out is different to what I ordered, I just want what I ordered.

I understand that OP but I don't understand what advice you're looking for here?
Have you sent the seller the first photo shown in your OP?

I've sent him several pictures, he says the backpack is silver holographic, I can see it is pink based holgraphic! I wanted to know if other people thought it looked pink....not much point in me swapping if it will be another pink one or just plain silver.

I think the smaller one looks more pink than the bigger one. Is that what you mean?

It looks silver to me. The bum bag looks blue.

The one in the listing that you picked has a pink and a blue element to it like those car paints that have different colours depending on the light. It doesn't say 'silver' in the description, just holographic. It's a bit monitor-dependent but the one you've got is a lot paler than the one that is advertised as pink.

If you look at your own picture that shows your laptop, the bit of bag you can see looks silver and blue. I think it is the one that you ordered.