The most likely cause is dust on the camera sensor, not on the front of the lens. Sensor dust often appears as a soft dark spot in the same area of images, and it becomes more noticeable at smaller apertures. Since many kit lenses use a smaller maximum aperture when zoomed in, that can make the spot stand out more.

To confirm it, stop the lens down as much as possible and photograph an evenly lit white sheet of paper or a plain bright surface. Dust spots should become easy to see.

If that test shows the spot clearly, the sensor likely needs cleaning. The blue tint issue sounds unrelated and would be better handled as a separate question with an example image.