Red means Lead!
One of the legacies for buildings built before 1972 is that the paintwork, that is oil-based paints, that we used on the house or any building will contain lead.
Lead paints were available up until 1972, following that time any domestic paint had to be manufactured lead free.
There is a test that can be carried out using a lead testing kit that will provide an answer as to whether or not the enamel paint in your home contains lead.
The first picture the result of a lead test that proved positive, tip on the testing vial clearly shows that there is lead present the coating.
The second picture shows the area that the test was taken which was in this case exterior windows on a building built in 1960.
The problem here was that the existing paint system had failed exposing the lead laden oil-based paint underneath and when re-coating was to take place it meant that sanding back all the way to remove the old and flaky paint would expose the lead paint and therefore safety issues that can occur.