I've been trying for a few hours now, and I've done a bunch of searching, and I'm really not sure what it is I'm doing wrong.
I used this code:
function drumath_settings() {
$form['Grid Color'] = array(
'#type' => 'textfield',
'#title' => t('Default color'),
'#size' => 12,
'#default_value' => '#d6d6d6',
'#validate' => array('is_valid_hex_color' => array('Grid Color')),
'#description' => t('Choose the color of the graph grid.'),
);
$form['Frame Color'] = array(
'#type' => 'textfield',
'#title' => t('Default color'),
'#size' => 12,
'#default_value' => '#eeeeee',
'#validate' => array('is_valid_hex_color' => array('Frame Color')),
'#description' => t('Choose the color of the graph frame.'),
);
$form['Canvas Color'] = array(
'#type' => 'textfield',
'#title' => t('Default color'),
'#size' => 12,
'#default_value' => '#ffffff',
'#validate' => array('is_valid_hex_color' => array('Canvas Color')),
'#description' => t('Choose the color of the graph canvas.'),
);
$form['Border Color'] = array(
'#type' => 'textfield',
'#title' => t('Default color'),
'#size' => 12,
'#default_value' => '#000000',
'#validate' => array('is_valid_hex_color' => array('Border Color')),
'#description' => t('Choose the color of the graph border.'),
);
$form['Scale Color'] = array(