We do not only see colors. Like this red dress, black cat, hazel eyes. When we close eyes and think about color red we see so much more. So we can explain color by comparing it to some thinks that blind person may know about. One thing that we can see are emotions. Actually they are usually both very intense, but extremely different: love and hate. We can describe color red as love, passion, infatuation, desire. When seeing lovers we may thing of red sort of halo moving with them. We can also see this kind of halo but maybe in darker shade around people in fight. When blind person will think of hate, anger, cruelty, ferocity. We can explain to this person that color red is like these emotions, very intense, after some time it may begin to bother us.
Color may also be explained to blind people as things that are typically red and they know how those things are like. A flame, burning wood, coal in the BBQ, are all red so it can be explained as something hot, burning. Another red thing is blood; we all have it in our system so fluid that runs through our veins can be one of explanations
Color red is also visible on traffic lights and on the stop sight. It can be seen as a sign to finish doing something or as the end.
Being blind does not mean that that a person does not see anything. It meant that this person just sees things differently. In my opinion those explanations may help blind people to understand what color red