Yellow Pen in dreams
An ink-bearing writing tool — the means of recording what you mean, in your own hand.
How yellow changes the reading
Yellow colour is the dream's attention itself — the symbol in yellow is the symbol the dream specifically wants you to notice. Sometimes it is warmth, sometimes warning, often both at once.
The base reading of Pen
A pen in a dream is the dream's image of the means by which an inner intention becomes a recorded line. Pens commit; what is written in ink is harder to retract than what is written in pencil. The dream brings the pen when something in your life — a decision, a confession, a signature — is ready to be put down in a form that will outlast the impulse. A pen writing cleanly is the dream telling you the moment of commitment is the right one. A pen that has run dry is the dream noting that the will to commit was there but the resource — energy, conviction, courage — has run out at the wrong moment.