This is a, ah, perennial question (see similar ones below), and there is still no sure answer that we are aware of. The color change could be a sign that the plant is aging, it could be an indication of not enough sunlight, and it could be symptomatic of poor soil conditions (inaccurate pH or lack of composted/organic material or lack of moisture; see above). We hope this helps!
This is a, ah, perennial question (see similar ones below), and there is still no sure answer that we are aware of. The color change could be a sign that the plant is aging, it could be an indication of not enough sunlight, and it could be symptomatic of poor soil conditions (inaccurate pH or lack of composted/organic material or lack of moisture; see above). We hope this helps!