This paper describes a scalable extension of the High Efficiency Video Coding (HEVC) standard that supports different color gamuts in an enhancement and base layer. Here, the emphasis is on scenarios with BT.2020 color gamut in an enhancement layer and BT.709 color gamut in the base layer. This is motivated by a need to provide content for both high definition and ultra-high definition devices in the near future. The paper describes a method for predicting the enhancement layer samples from a decoded base layer using a series of multiplies and adds to account for both color gamut and bit-depth changes. Results show an improvement in coding efficiency between 65% and 84% for luma (57% and 85% for chroma) compared to simulcast in quality (SNR) scalable coding.