how to change this color display?

Hi,

You want to edit the email via the menu System>Emails. There, you'll see the "template" setting with an edit icon. Click on that icon and it will open a popup where you can modify all of these.

Hi,

What did you change there ?
As I said, you need to change the template. In the template, you'll find all the CSS used:
monosnap.com/file/JegV2JaRagjVxcq5grQHjKFzoudJLB
The background color comes from this CSS:
body.hikashop_mail { background-color:#ffffff; color:#575757; }

You'll also find many "font-size:12px;" in there which dictate the size of the text in the email.

And for the color of the header image, you'll have to do your own image, upload it on your website, and change media/com_hikashop/images/mail/header.png to use that new header image instead of the default one.

Hi

I'm sorry but I don't understand how you get the result of your screenshot or what you want to do.
Did you do some code modification ? Or did you add the image of the email on the image of the thank you page screenshot ?
Are you saying you want to display the order details on the thank you page ?
Or something else ?