Is it really possible to compensate for colour blindness with a filter?

In the last 2 decades, there has been a resurgence of the idea that passive aids such as colour filters can be an effective solution to compensate colour vision deficiency (CVD) or improve colour vision for subjects with CVD. We examine briefly the scientific evidence that has to date been gathered to study the reliability of these aids. In the light of our experience working in this field, we reflect on several related issues: why this question has not been elucidated before, how a filter would have to be designed for a specific task, and the importance of developing a personalised colour space for subjects with CVD to gain some insight into the effect of aids.