Hello! If you're referring to the main info box's background colour then:

• Press CTRL + F then type in search "min-height: 640px; border: 6px solid;"
• After the ; add background: #ffffff or the hex colour code you want to use
• The line of code should now look like <div class="card rounded-0 p-3" style="min-height: 640px; border: 6px solid; background: #ffffff">

As for removing bootstrap's default colours that depends on what you need changed? If you're trying to customise text colour, you will need to add and remove a few things

• Press CTRL + F then search "text-muted"
• Replace ALL with nothing to remove it
• If you want to change the main text colour (excluding hero's status), you can add color: #000000 (or whatever colour you want) to the top line of code. The code should look like <div class="container" style="max-width: 820px; color: #000000;">
• This will however affect the border colour too. So if you want a different border colour press CTRL + F and search for "border: 6px solid" (there's only 2)
• Add a hex colour after solid. Code should look something like style="min-height: 240px; border: 6px solid #HEXCODE;

I hope this was not too confused. I tried to simplify it as best as I could ;__;