"colossal risk" is a correct and usable phrase in written English
You can use it when you want to emphasize a great risk or danger. For example: "John was taking a colossal risk when he drove his car through the flooded street."
A crash still represents a colossal risk, so Volvo's stated aim is to build cars which simply do not crash.
Contemporary art has overwhelmed the current market, but it is still a colossal risk, if only because there are so few standards to judge it by.
He is also, and this is the colossal risk Robinson takes, the hero of a science-fiction novel in which he escapes his own time to participate in one of the greatest of human adventures – one that threatens, yet again, to dethrone humanity from the centre of its perceived universe.
And why would any politician endorse this colossal scale of risk?
His life in and out of the theatre was picaresque, his energy boundless, his sense of opportunity discerning, his taste for risk colossal.
Indeed, given the risk of colossal upheaval that would follow meltdown in the eurozone, there is a fair argument that the ICB has been lenient.
The expense of human space flight is enormous and the risk of failure colossal.
But the curators create like the artist; they stick their necks out and take risks on a colossal scale.
Focus only on more rules and the medium-term risk is of a colossal, semi-socialised banking system crawling with outgunned, possibly captive regulators.
Reliance on investment, usually aided by state-owned banks with a poor understanding of risk, has led to colossal waste and overcapacity.
Blankfein bluntly stated that AIG's "failure at risk management was of colossal proportion".
