You can customize the Contact Form 7 colors globally as well as from the Contact Form & Element .
From the theme options you can customize the following options
Contact Form Font Color – Select a color for the Contact Form Text Color
Contact Form Border Color – Contact Form Input field Border Color.
Input Field Background Color – Contact Form Input field Background Color.
Input Field Focus Color – Contact Form Input field focus Color.
Button Text Color – Contact Form Button text Color.
Button Background Color – Contact Form Button Background Color.
Button Hover Background Color – Contact Form Button Background Color.
Button Border Color – Contact Form Border Background Color.
Button Hover Border Color – Contact Form Border Background Color.
