Q.red hibiscus tree
My hibiscus tree flowers but the end of the flower turns black along the edge? What is happening?
The flowers of a Hibiscus last about 24 hours. As the flower fades the edges of the flowers will roll and began to fade. This may cause the color change, to darken and appear black or even blue in the case of a red Hibiscus.
If you are dealing with insects, disease or watering issues, the leaves are the best indicator of issues.
I believe your plant is just fine and growing and acting normal.
Here are some links to refresh you on the care requirements.
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/deadheading-hibiscus-flowers.htm
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm