The concept, that mood and certain emotions (when experienced) cause a wide range of specific cognitive processes and biasses, is widely accepted in the affective sciences.
Mood congruence is part of this literature.

Positive emotions (e.g. elation) recall positive memories significantly faster. Negative emotions recall negative memories significantly faster. This is demonstrated by numerous experiments such as the one where participants were induced into a happy mood and then recalled significantly more pleasant events of their childhood, yet when induced into a sad mood, they recalled significantly more unpleasant events.
Anxious people respond faster to threats, yet a trade off exists of responding more slowly to non-threatening material when highly motivated to detect threats.
Attention biassing of high-trait-anxiety persons, which is typified by a vigilant disposition, can be dependent upon the temporal closeness of a perceived threat (e.g. normal attention at non-exam periods verses high attention biassing for negative exam-related words immediately before and during exam time).

Our conscious attention typically focuses on one thing at a time while expanding to a few at a time when stretched. Such laser beam precision is set in an all encompassing body of knowledge that is so vast that any one experience is dwarfed into appearing as an atom-like piece of a star, so this begs the question “how do we decide what one thing to focus on when any single event is reduced to such insignificance?” When there are a billion things to choose from, what helps us order our thoughts to focus upon a single event or a succession of single events so as we form a working model of what’s happening in front of us?”
A part of this mesmerising process of ordering chaos is an evolved instinctual psychological routine to help us assess what we perceive. Every single experience is constructed of many different parts of awareness (such as specific emotions, cognitions, sensory stimuli etcetera) which form the basis of what we then call our mood. Each single mood experience has its own flavour and intensity, so our present experience can be matched to a colossal vault of memories, and those with a similar tone and intensity can be brought to the foreground of awareness. Thus we can consciously peruse through similar experiences to see if our past experiences can help us more accurately identify what’s happening in the present in order to make better decisions.
This process is called mood congruence, and this part of the process denotes how implicit memories are retrieved automatically. Although this process has evolved to aid us, it can also keep people with mental health issues effectively strapped into thinking about similar negative thoughts and emotions which are causing them so many difficulties. Such mood congruent implicit memories are now of interest to the affective sciences which enquire into mental health issues.
Mood congruent implicit memories which are retrieved create a further mood modification which logically would bring their own affect infusion into the mix.

The methods of this innate heuristic when searching internally through an associative network of experience – to quickly access relevant contextualising information from a vault containing billions of particles of stimuli – seems to be the base for how we search for relevance in the external environment too.
For example, when anxious people are choosing articles to read they may select threatening content and be drawn to threatening words in that content. A perhaps more understandable example is of people with snake or spider phobias who are hyper attentive to anything which could be construed as their feared thing, yet neither are hyper sensitive to the other’s feared thing. Thus people who have a phobia of snakes are hyper sensitive to snakes, and people who have spiders phobias are hyper sensitive to spiders, yet snake fear does not make people search for spiders and vice versa.
This may sound an obvious statement, but the mechanisms by which this is achieved are revealing of the associative memory network which must exist for this to happen.
The concept of mood congruence is thus rooted in an associative network of memories.

Mood Congruence