Here is today's progress thus far. It is a bit of a mess as I wasn't sure what I wanted in the background and I often lose my way with the flower petal and leaf shapes. I've noticed too that I have not left any white within the flowers. The background in the upper left (viewer's left) is actually a bit lighter and less saturated than what is showing here. One other thing that I noticed are the two red petals in the lower right "kissing", so will correct that too. I have to say I am really enjoying painting this as it is a challenge plus painting on larger paper is a joy.
The top photo shows the corrections made in Photoshop. I used Levels to lighten then desaturated the photo as well as decreasing the blue in the mid-tones and shadows. I also used the Transform-Skew button to straighten and square up the photo. Below shows the original photo, taken under a mix of fluorescent, incandescent and natural light.