what does a rainbow round the sun mean?

It may either be a halo or carona.Halo is formed by the refraction of light by ice crystals in the cirrostratus cloud..It is believed to be an indicator of approacing storms even though it does not become true always.

Carona is produced by the diffraction of light by water drops in the altostratus cloud.The colour sequence will be different between halo and corona.The red of the halo will be inside and that of the carona outside.

It's way way far from Mr. Sun and pretty close to you although the effect gives the illusion something is up at the sun

Depending on weather condition, really small water droplets suspended in the atmosphere typically some ten miles or so away from you are acting on the light in its path getting to your point of observation.

Sunlight is still white light on the other side of those fine water vapour (droplets.) The sunlight is made up of all the colors of the rainbow and it looks white until it is "split" into component colors,

as a prism only uses water vapor as a huge collective prism.

Incidentally, (pun intended) the sixty-degree incidentangle called the Bragg angle, of the sun's light to the "rainbow" image from point of observation is always at sixty degrees about the circle visually surrounding the sun even though the image occurs where that moisture is.

You'll rarely see the phenomena at sun rise or sunset, but rather when you're looking (nearly) straight up . ( Happens with the moon too)

A rainbow, or a halo around the sun, is created by a thin cloud made mostly of ice crystals. This is commonly called a cirrostratus. Usually they appear when moist and warm air is lifted over cold one along a polar front. Because of that, they are usually seen at the beginning of a warm front and can be the forerunners of a low pressure moving in.

Best regards from Norway, nearly at your antipode! :-)