why does h1 color is red in bootstrap code example

Example 1: bootstrap 4 bg

.bg-primary
.bg-secondary
.bg-success
.bg-danger
.bg-warning
.bg-info
.bg-light
.bg-dark
.bg-white

Example 2: bootstrap 4 bg

.bg-gradient-primary
.bg-gradient-secondary
.bg-gradient-success
.bg-gradient-danger
.bg-gradient-warning
.bg-gradient-info
.bg-gradient-light
.bg-gradient-dark