My initial thought is
yellow
but I can't make all the clues work.
Solid round the number 1,
The #1 billiard ball is a solid yellow, and "solid" is a term from billiards.
This clue may also indicate wordplay (a synonym of "solid" around the letter 'i'), or refer to some game where a "solid round" would be a score of 1 (for instance, golf).
A motley few, this road, walked on,
Assorted billiard balls roll around the table.
Yes I'm a coward now be gone,
"Yellow-belly" is a synonym of "coward".
Made of two but I am one!
There are actually two yellow billiard balls: a solid and a striped.
This may also refer to the fact that the word "yellow" is composed of the words "yell" and "ow".
Submersing ship with unhinged crew,
A submarine is a "submersing ship" and the paradigm submarine is yellow (think the Beatles' album Yellow Submarine).
Twixt 'Of' and 'Gave' another clue,
Not sure about this one, but there is probably an idiom or phrasal verb having the form "gave __ of". For instance, "gave evidence of".
Never in a shade of blue,
Perhaps a literal reading: yellow is never blue.
I warn of danger, please don't sue!
Yellow often symbolizes danger (think traffic lights or yield signs).