The Roman navy, despite performing vital logistical duties from Iraq to Ireland and integral to the Pax Roma in the Mediterranean for century after century, was quite often sneered at by the more conventional Roman soldiery. It was less like the US Navy or the UK's Royal Navy and more like the US Coast Guard (or the US Army's logistical/transport "navy").
Yes I agree. You know I think you are onto something though with the colours as the period was one redolent with colour and tone. It is shocking to our modern eyes. The addition of dirt and wear is the way to go, I think, though: rough men in worn-out clothes, perhaps?