Lilac bonsai health query

This is a young lilac bonsai I got last year and which is currently flowering well, but I spotted that the leaves don't seem to look great. Not overly visible on the photo but basically the central part of the leaf is a normal shade of green or at least the shade I sort of expect tho perhaps a bit lighter than it should be, but the edge of many of the leaves has lost colour rather obviously.

Now, it's the first time I've had this particular form of lilac so don't know if this is normal or if it's missing something. It arrived last year in a peat mix but because the pot had been damaged due to a very delayed delivery (3 wks + despite being Next Day delivery, thank you Royal Mail), I opted to remove about half of the soil and potted it up into a bonsai grit mix. Since then it's been fed fortnightly with alternating Green Dream pellets and a Seaweed liquid feed.

Am I worrying about nothing - is it true that if a plant of any kind flowers it's in decent health? It just cost me a fair bit to get and I don't want to risk losing it by making any assumptions on what's happening here (if anything). Thanks.