How to replace the thank you image check icon?

when someone submits a from the thank you comes up with a big green tick. Is there a way to change the colour of the tick?

You can but you'll have to replace the image. The check icon is an image loaded from this link https://cdn.jotfor.ms/img/check-icon.png. 

1). Create your own check image

2). Upload it in any image repositories online

3). Grab the URL and replace it in your Thank you page source code.

Let us know if you have any questions or if you need further assistance.