Hello Casimir.

The properties of filters is different. For example - the text filters (Athlete Name, Event, Enter School and Meet Name) are using placeholders. To change their color, you'd need to add the following CSS to Custom JS and CSS tab, under Custom CSS field (found in main settings of wpDataTables):

input.form-control.wdt-filter-control.text_filter::-webkit-input-placeholder {
color: white !important;
}
input.form-control.wdt-filter-control.text_filter::-moz-placeholder {
color: white !important;
}
input.form-control.wdt-filter-control.text_filter:-ms-input-placeholder {
color: white !important;
}
input.form-control.wdt-filter-control.text_filter:-moz-placeholder {
color: white !important;
}

The reason for adding this many CSS lines is that the commands are different from browser to browser. You can take a look at this link to read more about this. Also, you can check how different browsers handle placeholders at this link.

To change the color of drop-down filters, you would need to add this CSS to the Custom CSS field in main settings:

span.filter-option.pull-left {
    color: white !important;
}

Please try this and let me know if it helps.

Best regards.