They are block elements.
If you look at the HTML 4.01 strict DTD:
<!ENTITY % heading "H1|H2|H3|H4|H5|H6">
<!ENTITY % block
"P | %heading; | %list; | %preformatted; | DL | DIV | NOSCRIPT |
BLOCKQUOTE | FORM | HR | TABLE | FIELDSET | ADDRESS">
So, they are all defined as %heading
entities, which in turn are part of the %block
entities.
As for the question regarding if you can change the color - that's just styling and is fine, though I would do so in a CSS file, not inline:
H1, H2, H3, H4, H5, H6
{
color: #ccccc;
}
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