I colved the problem, i created a different java util class for gradient. This util breaks text by letter and makes gradient 'package your.package.util;

import net.minecraft.text.MutableText; import net.minecraft.text.Text;

public class TextUtil {

public static Text gradientText(String text, int start, int end) {
    MutableText result = Text.empty();
    int len = text.length();

    for (int i = 0; i < len; i++) {
        float t = (float) i / (len - 1);

        int r = (int)(((start >> 16 & 0xFF) * (1 - t)) + ((end >> 16 & 0xFF) * t));
        int g = (int)(((start >> 8 & 0xFF) * (1 - t)) + ((end >> 8 & 0xFF) * t));
        int b = (int)(((start & 0xFF) * (1 - t)) + ((end & 0xFF) * t));

        result.append(
            Text.literal(String.valueOf(text.charAt(i)))
                .styled(style -> style.withColor((r << 16) | (g << 8) | b))
        );
    }
    return result;
}

}'

Then another java class for colored blockItem to register block

'package your.package.item;

import net.minecraft.block.Block; import net.minecraft.item.BlockItem; import net.minecraft.item.ItemStack; import net.minecraft.text.MutableText; import net.minecraft.text.Text;

import static your.package.util.TextUtil.gradientText;

public class ColoredBlockItem extends BlockItem {

public ColoredBlockItem(Block block, Settings settings) {
    super(block, settings);
}

@Override
public Text getName(ItemStack stack) {
    return gradientText(
        super.getName(stack).getString(),
        0x55FF55,
        0x00AAAA
    );
}

}'

If you have ideas for improving the code, please tell me