My initial thought is

>! yellow or yellow billiard ball

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.

Submersing ship with unhinged crew,

>! Not sure about this one.

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,

>! Not sure about this one.

I warn of danger, please don't sue!

>! Yellow often symbolizes danger (think traffic lights or yield signs).