The entire block of code on the screenshot below represents the section enclosed by the rectangle on the screenshot below that.
To change the colour of the button, there are a couple of attributes to look out for.
The first one is the bgcolor (bgcolor="#000000") attribute which assigns the background colour and style (style="color:#ffffff") attribute where you can control the 'style' in this case the colour of the text through color.
On the code block below, the block wrapped around the blue rectangle represents the white space around the button while the block wrapped with the red rectangle is the actual button.
Changing the value of the properties within the red rectangle (above) changes the color of the button as seen on the example below.
In this example, we change the bgcolor to red and change the text colour to blue. The result is the screenshot below:
