You can use these stylesheet settings:
a {
color: blue;
text-decoration: underline;
}
a:active {
color: yellow;
text-decoration: none;
}
a:link {
color: blue;
text-decoration: underline;
}
a:visited {
color: purple;
text-decoration: none;
}
a:focus {
color: red;
text-decoration: none;
}
a:hover {
color: red;
text-decoration: none;
}
but in an email it would be better to use it inline.
Unfortunately this is not possible.
To prevent colors of changing at all you should use:
<a href="www.domain.com/path" style="color:#000000;text-decoration:none;">download</a>
By adding the color to the style of the hyperlink it will remain that color, no matter what.
The text-decoration:none; is to remove the underline, but you can also not use it, or use the value "underline".