The colour orange used in the dress in this painting during the time of its creation, was mainly used to represent the colour gold or as an eccentric statement, possibly having royal connotations as orange was the most similar colour to gold during this time. Using orange here also helps with the effect of natural light from the sunset in the background creating a warm feel to the painting. 
Today I would describe the use of orange in the woman’s dress to be a bold statement as the shade is very bright. The warmth of the dress and sunset giving a warm feeling and possibly security. Maybe the woman is sleeping in a random place wearing a colour this bright shows she feels secure and safe  doing so. Possibly because she is royal and feels no threat or harm.