There should be a solid stripe of color at the top of the replacement pad. It maybe a pale yellow that is not easy to distinguish (colors can vary from filter to filter) Sincerely, Honeywell Customer Care
This filter does not replace the Aprilaire Model 550.
This model is compatible with Aprilaire: 112, 136, 224, 440, 445, 445A, 448.
Hi Bert, we need more information about your system to determine if the Whole-House Flow-Through Replacement Pad will work as a replacement. At your convenience, please contact us at 1-855-733-5465, or through live chat at https://www.resideo.com/us/en/support/.