It's normal at this time of the year for many plants to lose their usual colouring, and less sun is the culprit.

Here's Aeonium rubrolineatum in summer - it's been outside in nearly full sun:

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And here's a head of the same plant when back inside for the winter for several months:

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It's almost always a matter of sun - later in Spring, gradually start exposing your plants to more sun, and they'll colour up as they did before.

I don't use a grow light, although many do. I don't think you need to refrigerate.

It would help if you could post pictures of your plants, then the specifics could be discussed.

Yeah, I'll second that. I have a handful of plants in a spot that only gets sun during the summer. The ones that could change all reverted back to green months ago.

CmC - That is one VERY beautiful succulent!

You don't say which succulents you are talking about, and whether you are growing outdoors or indoors. Some succulents such as many Echeveria species actually color up better outdoors in winter, while many of the Aeoniums with colorful foliage lose their color in winter, and regain it in spring as the light intensity increases. Most likely your loss of color is from reduced duration of daylight, especially if they aren't being grown outdoors in full day sun. Other succulents such as Crassula erosula cultivars can be as colorful in winter as summer if they get full sun and are not overwatered.

No simple "one solution fits all" for various succulents, it really depends on what you are growing and where/how...

I will say that it is difficult to grow many succulents as indoor plants in winter and maintain vivid foliage color without supplemental artificial light.

I eschew the use of lights, hence my maintenance of vivid foliage colour is no more, but it will be again.

It's not half-bad having plants changing colours, but I tell you, if the salon were to have lights, the plants would have better colours - the same sort of green is becoming monotonous. However, that too shall change in several months. The room's too nice to add plant lights to it, so they suffer for the sake of furnishings' vanities.

I tell my plants that we have to save the planet so they have to go green in the winter. We do not waste electricity the winter. LOL

I feel fortunate to be able to grow all my Echeverias and coloful Aeoniums and Crassulas outdoors year round here in northern California, so no need for lighting, and some of the best color on the Echeverias comes with a bit of cold in the winter. On the other hand, when we get too much rain all at once in winter, my Echeverias in particular can suffer in the ground from staying too wet.

Sun and more sun, given gradually so they will not burn, and they can burn from cold as well. Stress bring out the color, so cut down on the water. Aeoniums are winter cool growers and come from the Canary Islands. Tops curl up in the summer to protet from the sun. Do not water at this time. So put them in the shade this time of the year.