"colossal importance" is correct and usable in written English.
You can use it to describe something that is of very great importance. For example, "The project was of colossal importance to the company's long-term success."
For people who want to live a little longer, perhaps to see a new grandchild or simply through that most overwhelming of terrors – the fear of death – these cost-benefit analyses are of colossal importance.
The novelist told the French magazine that he believes "we are living in the darkest time I have ever known", with the rise of Islamic State of "colossal importance for the future of the world".
Considering the colossal importance of this trial's testimony and proceedings in persuading the world that at least one, unequivocally good and just thing came out of the invasion, the folly of allowing both to be disrupted and eclipsed by Saddam is coming to seem yet another act of culpable idiocy, up there with not having an exit strategy.
The Golden Globes are often seen as a cheerfully rackety outfit given colossal importance simply by preceding the Oscars, but they are also an institution that, in specifically honouring comedies, favours that lighter kind of movie which can be overlooked in the general solemnity of awards season.
Wes Anderson has always had a very particular way of creating these magical, specific worlds where emotional events of colossal importance occur.
Although no decision is expected before spring 2008, tomorrow's hearing is indeed of colossal importance, not only to the detainees in Guantánamo, many of whom are about to start their seventh year of imprisonment without charge or trial, but also to the government's assertion that it is entitled to pursue these policies without any significant judicial oversight.
The pay is low, the work never ends, and students and parents can sometimes lack respect a real shame given the colossal scope and importance of the task at hand.
The Bolshoi (Russian for "big") has always been a colossal monolith of patriotic importance and cultural prestige, yet behind its dancers' clenched poise there is suppressed agony.
Among sundry manganites, perovskite manganite is of particular importance due to its colossal magnetoresistance (CMR) [26].
Sir Paul, like some others who've experienced colossal fame, can't quite hide his air of self-importance, but onstage he connects with the audience in a big way and the audiences still scream.
Trying to divine its importance for the industry here is like trying to predict tomorrow's weather in Morecambe from a colossal windstorm on the surface of Pluto.
