One close-up rarely records an orchid well enough for later comparison. Take a picture of the whole plant, a front view of an open flower and a side view showing the flower's shape.
Keep the label in at least one photograph. Colour alone is unreliable when screens and lighting differ, and a familiar common name may cover several plants.
Include what happens outside flowering
Record the leaves and the overall habit while the plant is not in bloom. For many growers, the arrangement of the foliage is a large part of its appeal throughout the year.
If fragrance matters to you, make a written note rather than expecting the photograph to preserve it. Say whether you noticed it and under what conditions; do not turn one impression into a guaranteed description for every plant.
Avoid editing the image until the colours become dramatically brighter than the original. A pleasing photograph and a useful growing record have different jobs. Keep an unedited version so a future comparison is based on the plant rather than on how the picture was processed.
Related reading: Appreciating Orchids: Fragrance, Flowers, Leaves and Form.